Some folks say they are the same thing, reverb and delay (or echo). I don't. The thing we call reverb for use in a home recording studio is really 2 things. The first is like an echo, yes. That is you hear a repeat of the original sound at some point after the original reaches your ears. But the thing we think of as reverb is the fact that the sound lasts longer. It's like being in a large room (college stairwells had nice reverb when I used to play guitar in them:)) with stone walls. Technically the sound lasts longer because what you're hearing is a mish-mash of a bunch of echos from all over the place. But it all blends together for a very different sort of sound than delays or echos. To me, echos are what you hear when you yell something in a canyon like: hello...hello...hello...hello.
Anyway, here's an article that explains how you can use both to both delay and reverb to improve recordings: