A standard tennis court is 78 feet long and 27 feet wide for singles and 36 for doubles. The lines on the court indicate if the ball lands in or out of play which decides if a point is awarded.
In singles, if the ball is hit outside of the narrowest set of lines then the ball is out, however in doubles the ball can land anywhere up to the widest set of lines and be judged in.
When a player serves they stand on the service line, at the back of the court on their side, and hit the ball diagonally towards their opponent. The ball must bounce inside the square between the opponent and their side of the net for the serve to count. If the ball goes anywhere else then the player must serve again but one more mistake and the opponent will be awarded a point. During a serve if the ball clips the net but still lands in the designated area then the serve is retaken but the player is not forced onto the risky second service.