The Beast is the evil that resides within man. The children were all aware that such a beast exists, but none of them realized (except Simon) that it lies within them. Manifested in three forms throughout the story, the Beast constantly plagues the littluns--the least conditioned by society.
Ralph represents law, order, organized society and moral integrity. Throughout the novel he is constantly making commonsense rules for the boys to follow. As chief, he knows right from wrong. At the end of the novel he too realizes that man is not a kind creature by nature.
Jack (and his tribe) represent anarchy. Jack did not have the integrity to keep the Beast at bay. He is the perpetrator of all three deaths that occur on the island and wishes to spend his time hunting (killing) instead of helping Ralph with rescue.
Piggy symbolizes knowledge and morality.
Without Piggy to help Ralph it is very possible that Ralph may have lost sight of things and given in to the Beast. Jack, who, throughout the novel systematically removes the forces opposing him, is scornfully afraid of Piggy and eventually kills him to eliminate his moral influence on the group.
The Conch is a symbol of the high hand of authority. Used to call meetings, it is magical to the boys, who for the most part respect it. In the end, when it is destroyed, authority on the island is gone and Ralph is left to fend for himself.
The Signal Fire
The Signal Fire is a representation of commonsense and rescue from immorality. When the signal fire can no longer be lit, because Jack stole Piggy's specs that light it, its beacon of hope and knowledge is no longer present to guide Ralph who must...