Jesus was baptized. Since then, millions of his followers have followed his example. Baptism is a way for you to do the same and participate in a common experience with Jesus followers around the world.
Baptism is a way to go public with your faith to show others that you have started a personal relationship with Jesus.
Baptism is not necessary for salvation. It symbolizes the new life you began when you started following Jesus. It symbolizes your old life dying (going under the water) and your new life (coming out of the water).