- Service -

In game play, the player serving the ball commences a point. Standing so that the ball is held behind the endline of the table, with the ball in the palm of the free hand—over the table's height—and the racket in the other, the server tosses the ball without spin, upward, at least 16 centimeters (approximately 6 inches). In casual (non-tournament) games, many players do not toss the ball upward, however this is technically illegal and can give the serving player an unfair advantage. The ball must remain above the height of the table at all times. The server cannot use his body or clothing to obstruct sight of the ball; the opponent and the umpire must have a clear view of the ball at all times

He or she then must hit the ball from behind the baseline such that it bounces once on his or her half of the table, and then bounces at least one time on the opponent's half. If the ball strikes the net but does not strike the opponent's half of the table, then a point is awarded to the opponent. However, if the ball hits the net, but nevertheless goes over and bounces on the other side, it is called a let (or net-in). Play stops, and the ball must be served again with no penalty. A player may commit any number of lets without penalty.

If the service is "good", then the opponent must then make a "good" return—by returning the ball before it bounces on his or her side of the table a second time. Returning the serve is one of the most difficult parts of the game, as the server's first move is often the least predictable—due to the numerous spin choices at his or her disposal—and thus most advantageous to him or her.

source: wikipedia.org