Baptisms in the Bible were by immersion. The original word for baptism most often referred to being immersed or submerged in water. Jesus was baptized by being immersed in the water and rising out of it (Matthew 3:16, Mark 1:10).
Submersion in the water symbolizes the death, burial, and resurrection of Jesus (1 Corinthians 15:3-4). Being submersed underwater represents our death to sin and the old way of life, and being raised out of the water is a picture of how Jesus raised us and gave us a fresh start in life (Romans 6:3-5).