Jack's first move is to not allow his choir members to join the congregation until he says so. This starts to reveal how he needs to be in control and gets very abusive and angry towards his group.
He then yells at Simon who he says is just trying to get attention, when he is probably in shock from the plane crash that they were just in.
Then Jack starts calling Piggy fat, and starts the entire group laughing at him. I think that these scenes were supposed to show how Jack represents evil and hate, and I also think that he represents Fascism because he inspires his followers through vague promises, rules through terror, and believes that he is superior to Piggy because Piggy has physical disabilities. I think that the time period is very important, because it was written right after WW2.