John the Baptist was a preacher who would preach about the coming of Christ and the need to be baptized to free yourself of your sin. He is often credited for paving the way for Jesus. He preached God’s law and about the coming of the Christ (Mat 3:1-6).
Before Jesus came on the scene John was there preaching and baptizing people. People would go out to the desert to see John and would confess their sins and get baptized by him. The whole reason for baptizing is just symbolizing that you are going to start a new life and your old life has left or been cleansed in the water.
John the Baptist met Jesus for the first time and baptized Jesus! Jesus asked to be baptized by John even though He had no sin to really free Himself from. But it was done in obedience to God’s word. I’ll explain this in the next question!