It is used to propel the ball from one side of the court to the other without touching it more than once. Since it is the first attack, it is important to learn how to execute a competitive serve which will make the opposing team lose the point or at least challenge them.
There are different ways of doing the serve, the underhand serve, which is mainly used in uncompetitive volleyball and by younger athletes, the overhand serve, which takes a while to understand how to do but which is generally simple, and the serve with the run up and jump, used by most professional athletes, as it is the most challenging. On the left you can see an athlete perform a good overhand serve in slow motion.
We are going to look at the underhand serve as it is the simplest and most versatile. You should place your feet less than shoulder-width apart with the non-dominant one forward.
Then crouch slightly and bend forward, your non dominant arm outstretched with the ball in your hand. Then you are going to hit the ball with either the palm of your hand or the flat part of your wrist. Look at the two videos to see an underhand serve in motion!
Most importantly, notice that they don't put much strength in their throw. It isn't needed! The ball is very light, and just by hitting it in the correct place, it will move to the other court easily.
Beware of not hitting the ball with your fist, as the throw will generally result in ending off court. Other mistakes you should avoid are hitting too harshly or too softly and you should start off by aiming straight ahead of you. Your first aim (if you are a beginner) should be simply to throw the ball over the net and into the opposing team’s court, without worrying about the speed or power of your shot.
As your skills advance, you should aim at serving on the sidelines or close by to certain players which might receive the ball badly and give you an advantage. Next, you will work on the speed and strength with which you hit the ball. But for now, just get the ball across!