to simply answer the question about what baptism is, metalman hit it right on the head.

Its a practice to show that you are laying down your old life and being raised up with a new life with Jesus Christ. Soooo... you are laying down your old life, which was yours... the life you knew before was yours.... and now.... you are raised with a new life... so the life that you once had is now gone, laid to rest, while the new life is no longer yours but is Christ's life... so you no longer live for yourself, but for christ.