How do I win this game?

How do you explain this game to someone who has never played? Here is what I say.

I usually tell my players, before they even roll up their characters, that the thing that I like best about Dungeons and Dragons (D&D) is that it is different from most games. In almost every other game, for me to win, you have to lose. D&D isn’t like that. You play a character that adventures with other characters. At its simplest, you go into a dungeon, find treasure, fight monsters, and try to get out alive. All of the characters help each other, and it often requires the help of each other for any of you to survive.

The Dungeon Master (DM) is kind of like a referee. He knows the layout of the dungeon and where all of the monsters and traps are and describes to you what your character can see. You come up with a character that you want to take on the adventure. In every situation, you tell the DM what you want your character to do, and he does it. If there is any question as to whether your character can accomplish what he wants to do, the DM decides how easy or hard this would be and you roll dice to determine success or failure.  Most of the rules are to keep the DM’s decisions from being arbitrary and to provide a framework for deciding how difficult it might be for your character to do things and what the result of success of failure might be. But the rules do not limit what your character can attempt.