The tremolo bar was originally only found on Fender guitars, but now they are on many types of electric guitar. Unfortunately, it has an inappropriate name, because "tremolo" means a fast succession of two different tones. A more accurate but less common name is the vibrato bar, and they are also known as whammy bars.
There are several different types of tremolo bars, details of which can be found in the Anatomy of the Guitar section, but certain types can only perform certain techniques. Thus, you should make sure the tremolo bar you have can do what you want it to do, before you buy it.
In general, it is good to learn to hold the tremolo bar between your third and fourth fingers, so you can use the bar and hold a pick at the same time.
This section will provide a description of how to accomplish various techniques, but it will be up to the guitarist to discover how to perform them.
A Dive Bomb may be achieved by striking a natural harmonic then lowering the tone. An "explosion" may added by keeping the bar pressed down and flicking the low E string repeatedly.
Also, there is an alternative way to do a dive bomb, by flicking a string, dipping the bar down, tapping a harmonic, then manipulating the resulting note however you want. This technique is also known as a "Squeal", or "Dime Squeal" named after Pantera guitarist, Dimebag Darrel.
Dipping is a technique that allows you to make note changes a little more interesting. Before you change to a higher note, use the bar to quickly lower and then raise the pitch.
With this technique, a pitch is held for a beat, and then raised up a tone. The lever is moved slowly, and once you reach the upper or lower tone, you immediately hold, and then reverse direction. This results in a sound that can sounds remarkably like a cat.
If you press the tremolo bar down, and then suddenly release it upwards and quickly alternate between high ups and down, it makes a snap-away sounds, like a ruler vibrating off the edge of a table. The principle behind this is similar to the cat purr.
The "windmill" develops if you just keep turning the tremolo bar in a circle. Naturally, the tone moves up and down at a regular pace. However, this can sound very "outer space" and can easily be over done, and you should use this sparingly.
If the strings are really slack, you can quickly whip the tremolo bar back up until it clicks, making a string choke. Sometimes overtones will remain, and you can get some interesting sounds and harmonies. However, these tend to disappear quickly as it is drowned out by the harmonics of the new string pitch.