There is no difference between the two. The wording is different sure, it's written by two different authors so that is to be expected. However, the story is still the same. Jesus is baptized by John in the Jordan. It's common knowledge where John was preaching and baptizing others, so it's not necessary for Luke to include that information. The stories are still the same, even if Luke doesn't specifically state the location of the baptism or who performed it.
Mark 1:9-11 "At that time Jesus came from Nazareth in Galilee and was baptized by John in the Jordan. As Jesus was coming up out of the water, he saw heaven being torn open and the Spirit descending on him like a dove. And a voice came from heaven: 'You are my Son, whom I love; with you I am well pleased.'"
Luke 3:21-22 "When all the people were being baptized, Jesus was baptized too. And as he was praying, heaven was opened and the Holy Spirit descended on him in bodily form like a dove. And a voice came from heaven: 'You are my Son, whom I love; with you I am well pleased.'"