...and a ball.
Then you need a reactangular space...
...and some net.
Put the net across the middle of the rectangle, starting at the middle point of both of the longest sides.
Now you need a friend.
|No, a human friend.|
That's better, though a smart man would have
chosen a female.
Okay, you're ready to play.
Take a racket each and stand at opposite sides of the net. Hit the ball to each other. There is a scoring system in tennis but it has really complicated numbers. Just take one point every time the other guy misses the ball. Make it that the first person who gets to 10 (or some other number, depending on how long you want the game to last) wins.