The boys plane crashes and they are stranded on a deserted island. When they all swim ashore, the boys find a conch shell and use it to call the others. The conch is a symbol of civilization for them.
The conflict begins when the boys divide off into different sides. Jack started his own tribe with other boys, while Ralph, Piggy, Sam, and Eric were still trying to use the conch to bring civilization. Ralph's side wants civilization, but Jack is more focused on hunting and survival.
On Ralph's side, they are trying to make a fire, but they can't because Jack stole Piggy's glasses. Ralph's group decides to go over to Jack's group and demand Piggy's glasses back. This leads up to the climax.
When Ralph's group is demanding back Piggy's glasses, Jacks tribe starts fighting them. One member of Jack's tribe throws a giant boulder at Ralph, but Ralph ducks and it does't hit him. Piggy, who didn't have his glasses, couldn't see the boulder coming in time for him to move. The boulder kills Piggy.
Sam and Eric were now captured by Jack and his tribe. The twins told Ralph to run away, so Jack couldn't get him. Meanwhile Jack knew Ralph was hiding, so he set the forest on fire to get him out. Ralph was very scared because Piggy had just died and now he was being hunted down.
When the forest was on fire, a naval officer saw and went to the island to rescue them. The boys saw him and immediately started crying. Seeing this officer reminded the boys of the real world. It made them realize what they have become, savages.