The final bid determines how a hand is played, who plays it and identifies the number of tricks that need to be made to make the contract. The winning bid team is the team who made the final bid.
The team that set the contract must make a base of 6 tricks plus what they bid to make the contract. For example, if the final bid was made by the North/South team, they will need to make 9 tricks (base 6 + 3 = 9) to make their contract. Since there are a total of 13 tricks (each player has 13 cards), East/West must win 5 tricks to prevent North/South from making their contract.
A trick is a set of 4 cards played, one from each player in turn. For example, North lays down a queen of Hearts face up from his hand. East follows with the 10 of Hearts, South then plays the 2 of Hearts, and finally, West plays the king of Hearts. West wins the trick since it was the highest card played. That is one round of cards played. Since West won that round, West will then lay the first card in the next round. This will continue until all 13 cards have been played; i.e., there are 13 rounds in one game and 13 tricks.
When playing a round, the player who lays the first card determines the suit that is played for that round. Each player must play a card of the same suit if they have one in their hand. If they do not have the suit that was led in the round, they can play any other card from their hand. The highest card of the suit led wins the trick. However, if a player does not have a card in that suit, they can play a trump card and the player who plays the highest trump card wins the round. The trump suit is the suit that was identified in the contract.
Author, Beginning Bridge by the Numbers