Blender 3D Reference Guide/Windows Reference/File Browser
The Blender File Browser is, of course, used to open Blender-native (".blend") files. It provides simple GUI widgets to navigate your computer's file system, and easy selection of files. The same basic UI element is used for the File menu "Append or Link" item, as well as, "Save As...", "Save Image...", and "Save Runtime..." menu items.
When "Open..." is selected in the "File" menu, the window that the cursor is over becomes a File Browser window. There are two text fields at the top for the currently selected directory, and the currently selected file. To the left, a button, labeled "P" will navigate to the parent of the currently selected directory. Also, there is a menu pop-up button which will offer directories from which files have recently been opened, allowing quick return to directories being used in the current project. To the right, there are buttons to open the selected file, and a "Cancel" button which aborts the File Browser completely, returning the window to its previous state. (Note that the "ESC" key can be used to abort as well.)
In the file list, which appears below these widgets, files that Blender recognizes are tagged with a small colored square icon to indicate that they may be opened. Depending on how many files are listed, there may be scroll bars for vertical and/or horizontal scrolling of the file list. The File Browser recognizes files with the ".blend" extension as compatible Blender files. It also recognizes ".blend.gz" as compressed Blender files (at least OSX version), and will open them, performing the decompression on-the-fly.
Like every Blender "window", there is a window "header", in this case, across the bottom of the window. The widget/icons here provide, in left-to-right order, the following additional function to the File Browser window: