This is a slightly edited version of the intro to RPGs I provided in the GURPS prospectus from Summer 2008. I thought it was worth repeating.
Once a character has been created and outfitted, players will control their actions in the game world, responding to the descriptions and plot developments provided by the GM, in order to solve mysteries, overcome enemies, gain prizes, and accomplish other objectives. At most points in the joint story-telling when success or failure of the character will be of consequence – escaping a ravenous lion, for example, rather than pouring a cup of coffee – players and/or the GM will roll dice. A die roll will determine whether your attack got through your opponent’s defense to do damage, whether you translated all or just part of a found parchment, whether you managed scale the wall of the fortress, or whether you dodged the boulder coming down the hill. Weighting based on the character’s attributes and skills will be added to the die roll to determine the success or failure of these kinds of actions by comparison to another die roll or a target number; the equipment that a character has will of course affect what the character can do and how easily it can be accomplished. In this manner, the overall direction and thrust of the adventure will be created by the players and the GM working together.
What the game actually looks like is a group of people sitting around a table telling a story together, occasionally rolling dice to see what happens next, and using small figurines and drawn maps (and sometimes other props) to keep track of the action on the tabletop. All character information is kept by the players and by the GM on summary sheets, and many players take notes as the game progresses. That’s why this type of gameplay is often referred to as “pen-and-paper RPG.”
Players work as team, cooperating rather than competing, in order to complete their mission(s), achieve goals, and, in the process, create a compelling story. The real enjoyment in RPGs is the role-playing: creating a character that is distinctive and interesting, and letting that character interact with the other PCs and with the NPCs that the GM plays.
A good team usually has a broad range of qualities and attributes: some muscle, some brains, some street skills, some diplomacy, and so on. Think of the system as similar to the A-Team or Mission Impossible model for characters: which member of the team do you want to be? The big, muscular guy who’s not too bright but very strong and courageous? The tinkerer, who can make devices and weapons out of junk? The con man, who can persuade people to believe any story? The acrobatic archer? Create your character, join your party, and get ready to adventure!