Related to the theme of leadership, Ralph shows how leadership and cooperation relate, what qualities a leader has to have in order to produce cooperation, and what the limits of cooperation are. When he organizes the boys, he shows how leadership can work with cooperative principles to build a society. This works for him because he's intelligent, good-looking, and charming. However, raw animal passion can overwhelm and disrupt cooperation, and when that happens, the leader's charisma is useless.
The wording of your question is somewhat confusing, but I am guessing that you are asking how does Ralph show cooperation as part of his leadership. Ralph begins to show cooperation right away in the first chapter when he accepts the role of leader. He immediately begins to assign roles to people, but the roles are ones that the individual boys want which shows that Ralph is working with the individual boys to put them where they'd be happy. Later, Ralph wants the boys to work together: some building huts and some hunting for food and some tending to the fire. Everything is for the good of them all. In chapter 11, after Jack and his tribe have stolen Piggy's glasses, Ralph still tries to urge cooperation among the boys when he, Piggy, and the couple who remain on Ralph's side confront Jack and the others.