There are two different set styles, the most common being the rock configuration. These have 12, 14, and 16 inch toms, usually a 22" bass drum, 14" snare, and 14" hi-hats. The other set-up is the fusion configuration. The toms are 10, 12, and 14 inches, the bass drum is usually 18", and hi-hats are generally 13 inches.
The rock configuration uses the bigger and deeper toms for a more full effect, a taller bass drum for a more "punchier" feel, and 14" hi-hats for a controlled splash. Some rock sets even have larger toms, so that there are 2 floor toms.
Fusion sets, most commonly used for jazz, on the other hand, have smaller toms to create less of a punch, but the toms are only 2 inches apart from each other, so they are more uniform. The Smaller bass drum and hi-hats are used for a controlled, responsive feel.
While drumming may just look like random smashing that takes no talent whatsoever, this is completely untrue. Drumming is in fact a talent, as it takes great co-ordination to have all four of your limbs doing different actions at once. Drummers also have to have great timing, since they are the driving force in a band's backbone.
Everyone else: you are now the "1337 machine" mon. We love you.