When you're serving in beach volleyball, you want to face your body into the court. If you're right-handed, you'll have your left foot slightly in front of your right foot.
Most right-handers tend to hold their ball in their left hand. You want to toss the ball in front of you, in front of your right shoulder, like this. When you get ready to serve, you're going to pull your right arm back, or your dominant hand, and you're going to toss the ball up, and contact it with a strong surface. You want your wrist to be strong, and your hand to be wide.
A very common serve is the float serve, and that means that you're trying to put a little pop on the ball with your hand. The ball basically doesn't spin but it kind of moves, and it will move in the wind, like this. Another kind of serve is a topspin serve, where you actually put spin on the ball. The ball will rotate like this, and it tends to drop in front of the passer.
When you do a topspin serve, you wrap your hand around the top of the ball, like this. When you do a float serve, you keep your hand straight and flat, like this. In beach volleyball your serve can touch the net as long as it goes over and in the court. And that's how you serve a beach volleyball.