Really?
(Mmmmm! Fresh blood...)
Basically... it involves several people usually sitting around a table. One is made Dungeon Master (DM) and leads the rest (the party) through character creation and whatnot. Then it is the DM's responsibility to come up with adventures (Either from their own mind, or premade campaigns you can buy at a store). The DM describes what the characters see, and the players hold conversations with each other and NPC's (Non-Player Characters, played by the DM), go on quests, and whatnot.
Usually the adventure starts with a 'hook' designed to draw the party into the adventure. It can be as simple as the king making a call far and wide for adventurers, to something far more sutble (like I prefer to do things).
The DM leads the party through dungeons, battles, all that good stuff, and the players say things like, "I attack the kobold king with my longsword" or "I'm casting Magic Missile now" or perhaps "I read the scroll. Can I decipher the script?"
It's tons of fun, and usually the atmosphere is one of casual good humor... though there can be extremely dramatic moments as well. All in all, it's a great way to pass the time, especially with a good DM and people you've played with for a while. Your characters take on lives of their own and they almost become independent entities... I cannot recommend it enough.
Hope that answers your question. For more info go to
www.wizards.com and explore their site.