In "Lord of the Flies", how is the boys' behavior on the island similar or different to the adults in the outside world? I'm not an adult, so I...

The boys behavior on the island is similiar to adults in the outside world in many ways.

At the beginning of the novel the boys set out to make a democratic society with rules and regulations. They are friendly and civilied.  This is how most adult relationships begin in the outside world. However, just like in the outside world, things begin to fall apart as defects of society are revealed.

Golding himself has said that the writing of Lord of the Files was "an attempt to trace the defects of society back to the defects of human nature."

Golding uses the young children to represent the evils and defects that exist in society. We see this in our everyday world as well.  The struggle for power exists everywhere in the outside world.  Think of corporate America.  There is a constant struggle amongst people to get to the top.  Everybody wants to have complete power and will abuse the power they have (think of Jack) to gain more. 

The island and the boys are just one way to represent man-kind and the outside world.