What is the difference between confirmation and baptism?
Since confirmation is not taught in the Bible, and not practiced by the churches I have attended, I can only give my understanding from things I read. Confirmation is generally practiced by those churches that believe in baptizing infants. (Most of the time, they don’t even baptize/immerse infants, even, but sprinkle or pour water on them.) The “baptism” is either to take away sins the child is supposed to be born with (another doctrine not supported by scripture) or as a pledge by the parents to bring this child up in the church.
For those in the former category, confirmation is “a sacrament in which the Holy Ghost is given to those already baptized in order to make them strong and perfect Christians and soldiers of Jesus Christ.” (Catholic Encyclopedia) This implies that the gift of the Holy Spirit promised in Acts 2:38 does not come immediately on the one baptized.
For those in churches for whom baptism is a pledge by the parents, such as the Methodists, confirmation would be a ceremony at which the child accepts responsibility for his/her own faith. In this it would be a lot like a Jewish bar mitzvah.
In either case, what is called baptism precedes confirmation by several years. To those of us who believe that baptism is for forgiveness of sins to those who are old enough to believe and confess that Jesus died for their sins, confirmation is not necessary. When they reach the point at which others would “confirm” them, that is when they are ready to be immersed.