The deck of Chance Chess cards sits next to the chess board. It's your move, so draw a card. With your opening move you will probably hope to get a 'Move Pawn' card to start the game in a traditional fashion. If, for example, you get a 'Move Rook' or 'Move Queen' you will have to pass on your first turn because your rook and queen cannot move at the beginning of the game because all pawns block their way, and your opponent gets a turn. Get it?
Now it is later in the game and you have a chance to attack your opponents queen with your rook. You have drawn your 'Move Rook' card and move into attack position. In normal chess, your opponent would likely wipe your rook off the board with whatever piece controls that square, but in Chance Chess, your opponent must draw a card that allows him to take or block your rook attack. He may control that square with his queen, knight, and bishop, but if he draws a 'Move Pawn' card, and no pawn is in position to take the rook, he is out of luck. But now you have to hope for the 'Move Rook' card or the 'Move Any Piece' card to capture his queen.