Which side of the court do I serve from in singles?

Under Law 10, it depends on the server's own score:

• 0 or an even number: serve from, and receive in, the right service court.
• Odd number: serve from, and receive in, the left service court.

If the server wins the rally, they score a point and serve again from the other service court. If the receiver wins the rally, they score a point and become the new server, serving from the court that matches their new score.