AutoCAD is a high end CAD (Computer Aided Drafting) Program. It has a multitude of features which this book will try to address.
AutoCAD is a vector based drawing application intended for engineering purposes. Commands can be entered at a command line or through toolbars and menus.
AutoCAD drawings are saved using the DWG extension, and over the years this has become a standard format for exchanging technical drawings, to the extent that even programs such as Adobe Illustrator will recognise DWG files. AutoCAD also supports an even more widely recognised format called DXF which was specifically designed as an interchange format. Unfortunately, as AutoCAD has passed through numerous editions, the DWG format has upgraded to keep pace with newer features. The most recent format was released with AutoCAD 2012 and any files saved using this format cannot be opened by AutoCAD 2011, 2010, 2009 etc.
Basic drawing tools
Creates a symbol on the drawing that is tied to a specific point. It is defined by coordinates (x,y,z). It is not necessary to create points when you want to draw other geometric entities.
Like it says. The user defines two points and AutoCAD constructs a line between them. Shortcut "l" ....
Construction line tools
Ray = A line with a defined starting point with infinte length at a specified slope.
Xline = An infinite line with no start or end point at a specified slope. Base point can be snapped with middle point snap mode. Shortcut "xl"
Polylines are the main business of most drawings. A polyline is made of numerous lines/arcs/or both segmented together into one selectable object. Polylines are quite versatile and the PEDIT(Polyline Edit) command can be used to access & edit many of the features associated with them. Shortcut "pe"
Polygons are regular, multisided shapes such as pentagons, hexagons etc. When this tool is employed, AutoCAD requests the number of sides desired and then asks whether the shape is to be defined as sitting on a circle of specified radius, or by the length of a side. The objects created from this command become "Closed Polylines" and can be edited using PEDIT.
This is basically a quick way of drawing a four-segment polyline with four right angles. Shortcut "rec"
An arc is a circle segment. When using this tool the user can define the arc by selecting three points through which AutoCAD will generate an arc, or alternatively the user can define a center point, a radius and a range of degrees to fill.
The only variables here are radius and centre point. Shortcut "c"
Splines are a particular form of curve generated by specific mathematical equations. The user can select as many vertices as they wish, and AutoCAD will generate a spline curve that incorporates all these points. Splines are generally used for cosmetic purposes, as their mathematical complexity makes them hard to define from a technical design perspective. Shortcut "spl"
Basically an oval. Similar to a circle, except ellipses require a radius to be defined for both their vertical and horizontal components. Shortcut "el"
Hatches are area fills. They can be made up of a solid colour, a gradient (in later versions of AutoCAD) or more usually a specific pattern. Hatches can be applied to a particular object such as a looped polyline, or any enclosed area. They can be (and usually should be) defined as being "associative" which means that if the area in which they are contained is adjusted, the hatching will update automatically.
Inserts a text string into the drawing. AutoCAD uses two forms of text entry, single line and multiline. These are known respectively as DTEXT and MTEXT. DTEXT is very much a leftover from AutoCAD's early years and there is no real justification for using it's very basic system when the MTEXT option has features similar to a conventional text editor.you may also select command TEXT for undefined area.
Basic Modifying Tools
Erases the selected object from the drawing. Can also be activated by pressing the delete key on the keyboard. Shortcut "e" (not very helpful because there is delete key)
we also erases the objects by selected objects for example. select the objects which you want to erase and then select the erase tool and press key enter
Copies the selected object from one point on the drawing to one or more locations. The user defines two points and the object is copied using these two positions as base points. For example, the user could select 100,100 as the first point and 100,200 as the second point. This would place the copy 100 drawing units above the first. Points can either be entered using the keyboard or by clicking anywhere in the drawing. Shortcut "cp"/"co"
Creates a mirror image of the selected object. The user defines two points, along which autocad generates a "line of reflection" and the reflected object is generated across this line with all components reversed. The user is then asked if they want to keep or delete the original. One problem with the mirror command is that if any text is included in the mirroring operation, it too is reversed making it unreadable and ridiculous. To fix this, type "MIRRTEXT" at the command line and change the value to 0. Shortcut "mi"
An offset is like a copy but is more precise and must be used for certain situations as the result is likely to be slightly bigger or smaller than the original. For example, consider a line that represents the edge of a road. This line contains several curved segments, and you would like to make a copy of this line to represent the opposite side of the road. A direct copy won't work, because the radius of the inside of a curve is much tighter than on the outside. The offset command allows you to simply define how far away and on which side you would like the copy to be made, and AutoCAD will take it from there. Shortcut "o"
An array is a quick way of doing a lot of copying, as long as all the copies are arranged in a simplistic way. There are two types of array; polar and grid. For a polar array, Autocad asks the user how many copies they want to make, and requests a centre point and a number of degrees to fill. Autocad then sweeps round this centre point making copies of the selected object in a circular pattern. For a grid array, the user selectes how many rows and columns they require, as well as the spacings between them and Autocad instantly duplicates the selected object(s) as many times as necessary. Shortcut "ar"
Works exactly the same as the copy command except the original is deleted. Shortcut "m"
The user selects the object(s) to be rotated, a centre point, and defines the number of degrees to revolve through. The original is deleted, so if a copy is desired the polar array tool should be used. (Though, since AutoCAD 2006, a "Copy" option is included in this command, making it possible to retain the original objects) Shortcut "ro"
The object(s) are selected, and a base point and scaling factor are defined. An easy way of changing a drawing from metres to milimetres is to scale everything up by a factor of 1000.
Starting a drawing
Upon running the program, the user will likely be prompted with an option to open an existing drawing or start afresh using a template. Templates are saved using a DWT extension and provide a quick way to get started. Having selected a template or having chosen to start from scratch, the user finds themselves at an empty drawing and is free to input information. The main area of the program window is taken up by the drawing area. This is surrounded by toolbars, a menu bar and a command line. The toolbars and the menu bar work the same way as other Windows programs, but the command line is a little more primitive. It is a throwback to the earlier versions of AutoCAD which existed in a time prior to Graphical User Interfaces and all editing had to be done by typing in commands and specifying coordinates. Even something like zooming into an area required the user to input the coordinates defining the window around the area to zoom into. Naturally enough, none of this functionality has been removed, with the result that AutoCAD now has both a modern graphical interface and a less pretty but far more flexible command line system. The advantages of using the command line to control the program will become clear later.
Using object snap modes is crucial for accurate drawing. Drawing without them will result in misaligned entities and inaccurate lengths and positioning.
They can be accessed while using a command that asks the user to input a specific point, either directly at the command line, the OSNAP toolbox or by right clicking while holding the shift key.
Layout Space/Model Space
Layout Space is typically used as an area for drawing entities that are not real-world objects, but rather entities that are informational in nature (annotations, border and title block, notes, etc.) and therefore can always be drawn at the same size they will be printed at. It has been long-debated about the usefulness of Layout(Paper) Space, especially since AutoCAD introduced xRefs and the ability to clip them. Many users find working solely in Model Space an efficient method of working in CAD (ala Microstation), however both methods of working in AutoCAD have their pros and cons, and what method a user may choose will largely depend on personal preference and/or the preferred method of the company one works for.
Model space is basically "the real world". Everything is drawn at a scale of one to one (where meters, millimeters or inches are the preferred drawing units) and all drawing components are positioned at the correct distances from each other, regardless of what sheet of paper they may end up being printed on. The drawings may also be positioned on a specific coordinate system, such as a national mapping grid, in order to integrate accurately with other drawings.
Layout (Paper) Space
A typical Layout Space layout will consist of a standardized title block containing information about the drawing; drawing number, date completed etc. This title block will be drawn to accurately fit on a standardized sheet of paper. For example, a sheet of ISO A1 measures 841mm by 594mm. Thus, a title block for printing on such a sheet may measure 820 drawing units by 570. It can then be printed out at a scale of 1 to 1, and will fit on the page nicely.
All this is of course well and good, but how do we get the actual drawing information from model space into this titleblock? To do this, we utilize an item known as a viewport. A viewport is a shape (usually a rectangle but can be any shape) that is drawn into paper space. Think of them as a TV screen. Inserting a viewport into paper spaces "places a camera" into model space. You can change the angle of view, the scale factor and many other variables in the viewport settings. These changes only effect this one viewport. This lets you have, for example, one large viewport of a building site at a scale of 1:100, and right beside it another showing a detailed area at a scale of 1:10. It's the same building site, and it exists only once in model space, but it is represented twice in two different ways in the final drawing. The obvious advantage of this is any changes made in model space will instantly update in every viewport, keeping all your printable drawings up to date.
An important thing to realize about AutoCAD is that it is not some kind of digital drawing board. A lot of inexperienced users approach the program as if it was MS Paint for engineers, and end up creating horribly thought out and disorganized drawings that can cause no end of strife and frustration for those who may later be required to work with the files. Not only can badly created drawings cause ulcers to other AutoCAD users, they make it a lot easier for design flaws to sneak into the process. A little bit of pre-planning and some attention to good drafting practice might be the difference between a painless efficient project and a messy expensive rebuild.
The most important thing to understand is that AutoCAD does not, strictly speaking, create "drawings" in the classic sense of the word. The user should not consider themself to be making pictures or creating images. A much more useful and accurate way of thinking about an AutoCAD drawing file is as being a database full of information. The AutoCAD program allows the user to view and edit this information through a graphical interface. Thus, when drawing a line between two points, realize that you are entering two coordinates into your database. So if you want a line that links the points 200,500 and 600, 1200, then those should be the values you use. Do not, under any circumstances, just scribble down a line in a place that "looks" right. What kind of database user are you, to be inserting 199.9813 when you mean 200? If you want one line to begin where a previous one ends, then ensure they contact at EXACTLY the same point. You can use the "Object Snaps" feature to make this work properly, and there is no excuse for creating drawings that contain elements that look like they line up until you zoom in to micrometer scales and discover why those polylines weren't joining correctly or those hatches weren't applying properly etc.
The Layers Window
The LAYERS window should be the hub around which any moderately well thought out drawing should revolve. It is through the layers window that all data is organised and controlled. A layer can be thought of as being a transparent sheet overlaying the drawing board. You can have as many as you wish. It is extremely useful to separate as much data as possible onto separate layers. It allows you to have numerous "drawings" all existing together in the one file. When a layer is "turned off" all the information that was on that layer becomes invisible.
The Layers window can be opened by either hitting the layers button on the toolbar or by typing LAYER or LA at the command line. For a new drawing, the only layer available is the layer 0. This is a special layer which is required in all drawings. It is bad drawing practice to create linework on this layer. It should be used only for creating the components of blocks and inserting xrefs. (More on these later). New layers can be created by hitting the "New Layer" button. By default, Autocad will name new layers "Layer1", "Layer2" etc. It is advisable to rename the layer to match the content that will be drawn on it, e.g. BRICKWORK, STORMWATER_PIPES, STORMWATER_MANHOLES etc.
An extremely important aspect of the layers window are the columns for Color, Linetype and Lineweight. Suppose you create a new layer, and call it STORMWATER. Next you might select the color value of this layer and set it to Blue. Upon hitting OK and returning to the drawing, you might start constructing linework. You will notice that the layers toolbar has several dropdown boxes in it, again showing color, linetype and lineweight. If all is well in the world, the words ByLayer should be written in all these boxes. This means that if you have a line on the layer STORMWATER whose color is set to ByLayer, it will automatically be Blue. If you reenter the layers window and change the Color of STORMWATER to something else, everything on the layer whose color is set to ByLayer will automatically change. It is possible to set the color of an object to something other than ByLayer, by selecting the object and than opening the color dropdown box on the Layers toolbar. This is very rarely recommended though. Think about it. Suppose you are drawing lots of pipes all over your STORMWATER layer, and they are all showing up Blue. Now suppose that there is one particular pipe that you want to appear green, because it is made of steel instead of plastic or something. The cheap and lazy option is to just change that objects color to green, but this means that you have given up some control over that line, because now you can no longer edit its color through the layers window. A good rule to bear in mind is, if something is different enough to deserve its own color, then it certainly deserves its own layer. In this case you would make a separate layer (colored green) called STORMWATER_STEEL upon which you would draw this one line. You would probably then rename the original layer to STORMWATER_PLASTIC, in order to retain consistency and to make it easier for someone else to understand the drawing.
Linetypes are a method of defining the pattern in which a particular line will print out, whether it be dashed or dotted or numerous other styles. The default setting is called Continuous, which just means a standard uninterrupted line. However, cases will arise, in particular when printing in black and white, in which it will be necessary to differentiate between different pieces of linework. Defining linetype works exactly the same way as for color. It can be changed individually on an object by object basis, but it is almost always preferable to leave everything set to ByLayer and adjust the settings through the layers window. By default, the only linetype available when you start AutoCAD is Continuous. To make others available, double click on Continuous in the layers window. The box that opens will have an option to "Load". The following window should provide a good list of extra linetypes which you can load as you need them. AutoCAD doesn't load them all by default to keep file size minimal. An important aspect of linetypes is scale. All lines have a property called linetype scale, which by default is set to 1. However, different linetypes may be defined in different ways. For example: a dashed line may have gaps that are 100 units apart and nearby dotted line may have been defined with gaps of only 10. It would be necessary to change the linetype scale of the dotted line to 10 to maintain a degree of consistency throughout the drawing. Just to confuse things, there is another variable called LTSCALE that effects linetype scale in the drawing at large. It is changed by typing LTSCALE at the command line. By default it is set to 1. Changes to this value are on top of changes to the object linetype scales, so if a line has its linetype scale set to 20 and LTSCALE is set to 10, the line will appear to have a scale of 200. The advantage of this is it allows you to have the same line appearing in different viewports at different scales without the linetype scale distorting.
CADopia 8 is a software similar to AutoCAD. 
This section is to include information about AutoCAD clones that are free software.
FreeCAD is an OpenSource CAD/CAE 
A9CAD has a freeware CAD version. 
ProgeCAD 2009 smart! is freeware for non-commercial use. 
DoubleCAD XT 
- AutoCAD 2007 and AutoCAD LT 2007 Bible by Ellen Finkelstein
- AutoCAD 2007 and AutoCAD LT 2007: No Experience Required by David Frey
- AutoCAD 2007 For Dummies by David Byrnes and Mark Middlebrook
- Digital Drawing for Designers: A Visual Guide to AutoCAD by Douglas R. Seidler
- Exercise Workbook for Beginning Autocad 2006 by Cheryl Shrock
- Mastering AutoCAD 2007 and AutoCAD LT 2007 by George Omura
- Up and Running with AutoCAD 2010 by Elliot Gindis
Free AutoCAD Tutorials
CADTutor - Text and video tutorials. 
MyCADSite - Text and video tutorials.