Serving begins every rally, so it is one of the fastest ways for a new player to help a team. The first goal is not power. It is a repeatable ball that clears the net and lands in play.
Stand behind the line with a comfortable staggered stance and hold the ball in front of your hitting shoulder. Use a small, predictable toss. A high or sideways toss makes timing harder. Contact the center-back of the ball with a firm, open hand and a straight wrist, stepping toward the court as you swing.
Practice with a large target area, such as the middle third of the opposite court. Notice whether misses go short, long, left, or right, then change one thing at a time. Once the serve is consistently in, narrow the target. Control is the foundation for every more advanced serve.