Yo Reggae! Reverb can be used as an obvious effect, or to simulate the sound of a certain kind of room, especially on a track that was recorded in a dead room (vocal booth, drum room, etc.). If your room doesn't sound so good, you can take a closet and turn it into a vocal booth. Then what you have is a clean track that's flat/dead. Then ambience (a fake electronically created room) is added. Reverb is really just a very short form of delay, to replace the echo of sound reflected back from real objects. Or, you can really crank up a cathedral simulation as an obvious effect.
Reverb is like makeup. That ambience is what you might call "the natural look". That cathedral is more like KISS/Alice Cooper. The computer plugins are getting better, but most people still tend toward outboard units. Purists who record in Analog often use good old plate or spring reverb units. (great for kicking on stage). Increasingly, digital units are being used. Among the most popular reverbs are those made by Lexicon and TC Electronics, and there are of course, many others. It is almost always built into a decent guitar amp, and some reverb is almost always used on electric guitar.
My cheap favorite is definitely TC Electronics M300 ($200). It's a good analog to digital convertor, has a number of usable effects, and it's real easy to learn how to use. You absolutely will never regret buying one.-Richie
