The rules of tennis or tennis rules are pretty in depth, so we're going to go over a simplified version of them.
Getting the right to serve is decided by the flip of a coin, and if the choice of service or receiver is chosen, the opponent chooses which side to start.
The official tennis rules state that the server gets 2 chances to serve correctly, and they always serve to their opponent diagonally.
So if they serve the ball into the net or out of bounds on the first serve they still have another chance to get it in bounds.
Before serving, the server calls the score out, and they always says his score first.
There is 4 points to win a round - love, 15, 30, and 40.
Whoever gets to 40 first wins the round.
If the ball gets hit out of bounds, or into the net during play, the other person get the point.
If the ball hit the line, it is fair, and play continues.
The tennis rules also state several penalties.
Touching opponents ground, the net or posts or any other person or official in the game will land you a penalty.
Carrying the ball or catching it in the racket is also a penalty to stay away from.
If you hit the ball twice before getting it over the net to your opponent, you are going to receive a penalty.
The ball also cannot touch any part of the player other than their racket, so if it touches your arms or feet, you're going to get a penalty.
Throwing the racket to the ground or any kind of racket abuse is not allowed as well.
These are just a few of the rules - tennis has so many different "ticky-tacky" rules that it's almost impossible to name them all.
But these are enough to play with some friends.