In Coup, you want to be the last player with influence in the game, with influence being represented by face-down character cards in your playing area. Each player starts the game with two coins and two influence – i.e., two face-down character cards; the fifteen card deck consists of three copies of five different characters, each with a unique set of powers.
When you take one of the character actions – whether actively on your turn, or defensively in response to someone else’s action – that character’s action automatically succeeds unless an opponent challenges you. In this case, if you can’t reveal the appropriate character, you lose an influence, turning one of your characters face-up. Face-up characters cannot be used, and if both of your characters are face-up, you’re out of the game.
If you do have the character in question, you reveal it, the opponent loses an influence, then you shuffle that character into the deck and draw a new one, perhaps getting the same character again and perhaps not. The last player to still have influence – that is, a face-down character – wins the game!