The Bible tells us that after Jesus' death and resurrection, Christians began to publicly declare their commitment to Jesus by practicing baptism. the Bible also teaches that all new believers are to be baptized (e.g. Acts 2:38).
Baptism is a simple act—you stand or sit in water, go down under the surface, and come back up again. It's a symbol of dying and being reborn, which is a fitting way to symbolize the spiritual reality of becoming a new person in Jesus.