Every soccer game begins with a kickoff at the center of the field. A coin flip determines which team takes that kickoff, as well as which one takes the kickoff to start the second half. Procedures surrounding the kickoff are spelled out in the "Laws of the Game" drawn up by FIFA, the international governing body of soccer.
Before the game, representatives of each team meet with the referee to toss a coin. According to the FIFA rules, the team that wins the toss gets to choose which goal it will attack. The other team kicks off to start the game. In soccer, the team that kicks off is said to be "taking" the kickoff. At the start of the second half, the teams switch goals, and the team that won the coin toss takes the kickoff. Note that, unlike in American football, there really is no "receiving" team on the kickoff. One team is simply the first to put a foot on the ball; once the ball is kicked the first time, anyone can touch it.
Setting Up Kickoff
To set up the kickoff, the ball is placed on the "center mark," which is the midpoint of the center line, or the exact middle of the field. All players must be on their team's half of the field at the kickoff. Players on the team taking the kickoff can position themselves anywhere they choose, but players on the other team must be at least 10 yards away from the ball when the kickoff is taken. A circle with a 10-yard radius surrounds the center mark, clearly indicating the area that's off limits to the opposition.
At a signal from the referee, a player kicks off. The ball is in play as soon as the player's foot touches it. The ball must go forward on the kickoff, but it doesn't have to go any particular distance before another player on the kicking team can touch it. So the player kicking off could blast the ball downfield, or just tap it forward for a teammate. The player who kicks off, however, cannot touch the ball again until another player, on either team, has touched it. That means a player can't just start dribbling the ball downfield at the kickoff. If the kicking off player does touch the ball twice in a row, the opposing team gets an indirect free kick from the spot of the second touch.
Other Kickoff Situations
If the game is tied at the end of regulation and match rules call for an extra period, then that period also starts with a kickoff; a coin toss determines which team takes that kickoff. There's also a kickoff after every goal. When a team scores a goal, the opposing team takes the ensuing kickoff.