This game is simply the adult version of Apples to Apples which is a very popular board/card game for kids.  The themes are just much more adult.  I would compare it to a rated R movie due to the level of sexual content.  The game is played by one person picking a brown card and the rest of the players each pick a green card that they feel best fits the word or phrase on the brown card.  The person who picked the brown card picks the winner.  You continue on this until someone has played all their cards and is the winner of the game.