Just in case people don't know what we're on about, here's a sample of play from Dungeons & Dragons:
Example: Start the game with the GM telling you where you are and some general ideas about your surroundings, Such as: "You find yourself in a swamp. To the North you can see a house. To the West you can go further into the swamp. The East and South passages are blocked by dense growth".
Player 1: "I move to the North slowly, drawing my sword in case something attacks us."
Player 2: "How deep is the swamp water?"
Player 3: "Is the house in good repair?"
Player 4: "I move to the North, too."
GM: "The two of you begin to move north slowly, the mud sucking at your boots from below the water line. The water is about one to two feet deep; generally shin-deep. {Player 3}, you try to determine the quality of the house from where you are. Make a spot check."
Player 3, who is trying to see if she can do something that may or may not be feasible is asked to make a "spot check". She will roll a twenty-sided die (d20) and add her skill of Spot to the total. The GM, in secret, will determine a number that represents how difficult it would be to succeed; this is called the "DC". If the player's total is equal or above the DC, then the attempt succeeds. More detail on how this works can be found in the Player's Handbook or in the SRD (System Reference Document).
Player 3 rolls a 13 on the d20. She adds the +3 she has in Spot, giving her PC a total of 16 to see the condition of the house. The GM had made the DC a 10, as it was fairly easy to see.
GM: "Squinting at the structure, you see that it seems to be leaning a bit to the side, with boards on the windows. It is unlikely that anyone has lived there in some time, but as to any thing living there... well, you're not too sure."
This is hardly an action-packed sample but you should get the idea.
