Rhythm And Lead Guitar

So much terminology, so many things to learn - rhythm guitar, lead guitar, drums, bass, the phone number of the drunk chick in the front row. Let's start with lead guitar. The lead guitarist is the dude who plays the tunes. When the singer stops singing, and one of the guys with guitars starts playing a bunch of notes, he's the lead guitarist. Sometimes the notes he is playing are what we call an "improvised solo". This means the guitar dude is making up the music as he goes along. He learns some sets of notes called scales, and he gets to know where on the guitar neck he needs to play his scales to fit in with the key of the song the band is playing. Sometimes he will be basing his solo, one way or another, on a riff or melody he learned from listening to, and trying to play, other people's music.
The guitar player who just strums chords is the rhythm guitarist. He learns the basic chords to the songs, sometimes adding chords of his own, and uses the srumming patterns of the song as the basis for his own interpretation of the song. So there's a little room there for the rhythm guitar player to do some creative stuff.
The lead guitarist needs to learn judicious use of the whammy bar and the effects pedals as well as lead guitar playing techniques like hammer-ons and pull-offs and using up and'or down strokes of the plectrum. But if you want to learn to play lead guitar, it's best to start with rhythm guitar techniques. The rhythm guitarist knows how the band works, he knows how to fit in with the drums and bass. If you know that stuff, then you can start thinking about putting yourself out front.
The lead guitarist will eventually need to get into some specialised areas of study: How to build finger strength, eliminating "dead notes", fretting tricky chords, how to maximize your picking speed, mastering chord symbols: how to read and play any chord symbol you encounter (like G7#5), how to solo with all seven positions of the major and minor scales, the modes, the pentatonic and blues scales, and how to write your own songs, riffs, licks and solos.
As for the rest of the band, the drummer plays the drums, and the bass player usually goes home with the drunk chick.
More info on learning to play lead guitar!