When you play bridge, if your partnership buys the final contract, the bidding determines who plays the hand (the declarer) and who kicks back and watches the action (the dummy). For example, if the final contract ends in some number of hearts, whoever bid hearts first becomes the declarer, and his partner is the dummy.

Take a look at this sample bidding sequence:

South (You) West North (Your Partner) East
1♥ Pass 2♣ 2♦
3♣ 3♦ 4♥ Pass
Pass Pass

The contract ends in 4♥, which is the final bid because it’s followed by three passes. Both you and your partner bid hearts during the bidding. However, you bid hearts first, which makes you the declarer.

The player to the left of the declarer (in this case, West) makes the opening lead, and the partner of the declarer (North) is the dummy. After the opening lead, the dummy puts down her cards face up in four vertical rows, one for each suit (with the trump suit, hearts, to the left), and bows out of the action.