I will interpret this question as asking which SIDE of the tennis court do you serve into first in tennis. The two halves of the tennis court are called "ad" (short for advantage) and "deuce." Your ad court is diagonal to your opponent's ad court and your deuce court is diagonal to your opponent's deuce court. You begin serving on your ad side diagonally into your opponent's ad side. If you are facing the net from the baseline, the ad side is the right and the deuce side is the left. In simpler terms, you start on the right side and serve diagonally into the left side of your opponent's court. This is a link to a tennis court diagram. Perhaps a visual will help better understand the answer to your question. It can be found on the related links.
Deuce side, otherwise known as the right side of the court.
Your first serve should be from the deuce side (that's the right side if you're standing on the baseline and looking at the net).
The opposite side, for example.... if you are serving from your left side, serve to the opposing teams right side.
A serve in tennis is when you have the ball to start a game. For instance, the score is 3-4 games, you with 3 games won, and it is your turn to serve. A serve is when you hit the ball on the opposite side of the court in the square. Example: Standing on the right side to serve, you hit it in the square on the left side.
You begin play by serving from the Right Side of the Court (known as the duece court) serving to the left.
The ad side of a tennis court is the players left side. Or the opponents right side.
In tennis, you don't serve on just one side. The first serve of each game will be from the deuce side (the right side if you are standing on the baseline) and the ball will be hit cross-court to the other player's deuce side. The next serve will be from the ad side (the left if you are standing on the baseline) and go cross-court to the other player's ad side. This alternation will continue until the game is finished and a new one starts or the match is over.
Deuce side, otherwise known as the right side of the court. This is the same for doubles, too.
A serve that does not land inside the service square on the opposite side of the court is called a fault. If it touches the net, then lands inside the service square on the receiving player(s) side of the court, then it is a let, in which case the serve is replayed.
On the first serve of every game you serve from the right side.
In tennis, a serve is when the player with the ball hits the ball into the opposite square from which they are standing in on the other side of the court. Example: Standing on the right side, you hit the ball in the square on the left side. In volleyball, a serve is when the ball goes over the net.