There are two types of serves in volleyball: Overhand and Underhand.
Overhand: The overhand serve is just as it sounds, you throw the ball up in the air and then you hit it hard to make it over to the other side. This serve is for more experienced players, because it takes a little bit to get the hang of it. You also need plenty of arm muscle to make it over.
Underhand: Underhand serving is when you hold the volleyball in your left or right hand (it depends on what your prominent hand is, if you're left handed you use hold the volleyball in your right hand, if right handed you use your left) then you swing it with your prominent hand.
Those are the two basically popular serves in volleyball, but it also depends on what serve you prefer.