Questions about the sport of volleyball. Beach volleyball should use the [beach-volleyball] tag.
Volleyball is a team ball and net sport, using an inflatable padded ball similar in size to a soccer ball and a net raised off the ground with its top edge at 8 feet. The sport can be played in a swimming pool (water volleyball, usually played recreationally by as many as are available), on sand (beach volleyball, usually played competitively in pairs or recreationally in teams) or on a hard surface (court volleyball, usually played competitively in teams of 6).
After one team "serves" the ball by sending it over the net with a single hit from behind the back line, teams each get three consecutive hits on the ball, no two of which may be made consecutively by the same player, to send it over the net to their opponents' side, where the opposing team then has the same three-hit opportunity. A "block" (a player raising their hands over the net to prevent the ball crossing it) does not count towards these three hits, however it does count as contact by that player when considering "double hits" and whose side last touched the ball. If the ball hits the playing surface in-bounds, the team on the side it landed loses the "rally". If the ball lands out of bounds, the last team to touch it loses the rally. Any player who touches the net with any part of their body during play loses the rally for their side.
The scoring of points has recently changed. Originally, points could only be awarded to the serving team; if the receiving team won the rally, they gained "possession" (the opportunity to serve) and the players rotated positions, but the side did not score a point. However, at most levels of play it is common for teams to alternate winning rallies, and so many rallies can be won without a single point being awarded. To speed play, this was changed so that the team that wins the rally always gets a point, with the receiving team also gaining the serve and rotating positions if they win. A competitive game or "set" is typically played until one team scores either 15 (in most junior or rec leagues), 25 (for adult women's leagues) or 30 (for men's leagues) points and is two points ahead; a team may win a "match" by having won two more sets than their opponent at any time, or by winning the fifth set (which is typically played to only 15 points).
There are three basic hits allowed on the volleyball besides various techniques used to serve the ball; the bump, made from just behind the ball's position by extending one's hands straight in front of the player with fists together or hands interlocked and hitting the ball with the forearms; the set, made from a position directly underneath the ball by hitting it nearly directly upwards with fingers or palms; and the spike, made again from underneath or nearly underneath the ball by hitting it forward and downward with an overhand palm or fist. These are the most controllable motions and thus are generally taught to athletes; however, any fair strike on the volleyball is allowed, such as a single fist from underneath. Players must not catch, hold or "lift" the ball during play.
To serve, two basic techniques are used; the underhand serve, used by recreational players, begins with the player holding the ball in the palm of their non-dominant hand and swinging the palm or fist of their dominant hand underneath it to hit it over the net. The overhand serve, used by most competitive players, begins with the player tossing the ball straight up overhead, and then hitting it with a palm or fist similar to a spike. The overhand serve is more difficult to perform accurately, but is much faster (at high levels of play a serve can exceed 70mph), and once mastered it it possible to add spin to the ball that causes it to curve off its initial line, similar to a baseball pitch, making such a serve more difficult to return.
In the U.S., court volleyball is played competitively beginning at about the 6th or 7th grade and continuing through high school and college. At these levels it is primarily a women's (girls') sport, although many high schools and colleges offer men's court volleyball in the spring in parallel with track and field. Sand volleyball is uncommon in school leagues due to the small number of players the game supports. Professional volleyball in the United States has had very limited success, although with recent rules changes to increase scoring, both beach and court volleyball are beginning to gain popularity in women's sports. Volleyball is played at the international level, with many international leagues for both beach and court volleyball, and both sports are currently featured in the Summer Olympics.