Ralph likes Jack. He also notices that Jack knows what his doing and decides that Jack wouldn't be too good as an enemy. As a way to satisfy Jack's urge to control, Ralph offers the choir to Jack.
He puts Jack in charge of the choir and asks Jack what he wishes them to be, to which Jack replies "Hunters."
When Ralph is elected to be chief he knows Jack is dissapointed (as Jack also wished to be chief) so he appoints Jack as leader of the choir and asks him what he wants them to be, to which Jack replies, "hunters."
When the boys elect Ralph as leader, in favour of Jack, Ralph puts Jack in charge of the choir and asks him what he would like them to be. Jack replies, "Hunters."
Jack and his choir were at the top of the mountain when Ralph spotted the smoke from the ship. They were supposed to be tending the fire, which they let go out while they were hunting.
When Jack and his choir first marched down the beach they stopped close to the platform and Jack, alone, vaulted onto the platform to speak to Ralph. When Ralph explained that they were having a meeting and said, "Come and join in." The choir began to scatter from close line. Jack shouted, "Choir! Stand still!" The choir obeyed.
At the time Ralph thought that he was offering Jack the consolation of being put in charge of the former choir, which Jack then decided would become hunters. Later with the perspective of hindsight Ralph may well have regretted that decision.
Ralph takes Simon and Jack along with him on the expedition.
In "Lord of the Flies," Ralph tries to make Jack feel better about losing the leadership role to him by allowing him to be in charge of the Choir Boys. Ultimately, this is a mistake, because it immediately separated boys who would loyal to Jack rather than him in the group.
Jack and his choir became hunters and helped Ralph and the others hunt for food on the island. However, they eventually broke away from Ralph's leadership and formed their own tribe, leading to a violent power struggle.
When Ralph is initially elected leader he confirms that the choir still belongs to Jack. Jack says that he wants his choir to be hunters, to supply the boys with meat by hunting pigs. After they light a signal fire on the mountain Jack says that his hunters will take on the responsibility for keeping the fire lit.
Ralph told him he could be the leader of the choir boys and then he made his own group of only himself until people from Ralph's side went to Jack's side. :)
Jack is the leader of the choir and the one who leads the break away group, who split from Ralph's lot to form a tribe.