This is a couple having fun together. The tandem bike is meant to be used by two people. The girl is holding to her friend instead of a bar because that implies they are having a intimate contact. The man goes in front to give the idea he is leading the bike, so he has to be more careful, they will go where he decides and how much fun they have depends a lot on his "driving". The general idea is that "coming together" is fun, as it is fun to ride a bicicle by two people.