There’s a Dungeons and Dragons for Dummies book out there, breaks it all down nice and easy.
Also, if you would like a good, basic roleplaying game, GURPS (Generic Universal Role Playing System) has a Lite version that’s freely downloadable:
For a good idea of how such games are played, check out Darths And Droids, a webcomic retelling of the Star Wars Saga in RPG terms..
Be sure to read the comments, as they do give some insight into how such games often unfold, and the way some players act. You may think the personality types in the comic are exaggerated for comedic value, but they’re not far off the mark in some cases.
(Oh, and some of the folks on the forum may be a little familiar…)