I've been a passive student o' the game for a long time, and I still don't know what defines the "ad" and "deuce" courts.
Also, where do you begin a service game? I've just been randomly picking a side, all this time.
The deuce court is your right side of the court, since that's where deuce points are played. The ad court is the left side of the court. You define what's left and right by what's left and right of the center hash mark.
You also begin serving on the deuce side. When you're on an even number of points played (15 all, 40-15, 30 all, whatever), you're always on the deuce side. When you're on an odd number of points played, you're on the ad side (15-0, 30-15, 40-0, etc.).
The game always starts on the deuce side which is the right and the advantage side is on the left. Odd numbers are played on ad and even numbers on deuce. We start at 0 so we're on deuce and when 1 point is scored, we move to the ad court and the score goes to 15 for 1 player. Next point won will be either 1-1, 2-0, or 0-2 so it's 15 all, 30 love, or love 30, which is played on deuce because it's an even number and so on. Tiebreaks are hard to understand for some so I'll explain that too. First server gets only 1 serve and his opponent gets 2 after that. They keep alternating 2 serves after the initial serve and that's why they play the 1st serve after the initial serve always on the ad side, because it's an odd number. I used to wonder why the server would start his serve from the ad court, but after I found out about the even and odd number rule, I got my answer.