Your first serve in a game is from the right side of the court. Your feet should be behind the baseline, between the center mark and the sideline. If your feet touch or go beyond either mark, you've committed a foot fault. The ball should go over the net and land in the service box that lies diagonal from yours. When either you or your opponent win that point, your next serve is from the left side of the court. Serves alternate sides for the rest of the game. If the ball hits the net but lands in the correct service box, you receive a "let" and can repeat your first serve. If the ball lands out of bounds, hits a net post or any other permanent fixture, your serve is a fault. Serving two faults in a row results in the loss of the point.
The ITF and the USTA rules require you to switch sides of the court with your opponent after every odd game in a set. You also switch at the conclusion of a set unless the set ended with an even number of games. If the number of games is even, you switch after the first game of the following set.
The name for zero points in tennis is "love." One point equals "15," two points equals "30" and three points equals "40." If you win four points, you win one "game." The first player to win six games with a two-game advantage over her opponent wins a set. To win a point, you must hit a ball that your opponent either hits out of bounds or into the net. If your opponent cannot return your shot, you win a point. You lose a point by hitting a ball into a permanent fixture, such as a net post, by double faulting and by letting a ball bounce two times before returning it.
If you and your opponent both score six points in a set, a tiebreaker determines the winner. To win, you have to score seven points with a two-point lead over your opponent. Instead of 15, 30 and 40, the points in a tiebreaker are standard numerals: 1, 2, 3, 4 and so on. Winning the tiebreaker means you've won one game and the set.