I assume that you are talking about what is found by Ralph and by Piggy in Chapter 1. What they find is a conch shell lying there in the shallow water.
At first, Ralph has no idea what to do with the shell. But Piggy suggests that they can use it as a horn. They can use it to notify anyone else who survived the crash that other people are alive on the island. This is the first use of the conch.
Later, the conch becomes the thing that shows whose turn it is to talk at meetings -- whoever holds it gets to speak.
After Ralph meets Piggy he and Ralph are exploring the island area around them. Ralph sees something under the muck sand. He leans over and wiggles it out of the sand. It is a conch shell. He blows the shell and to his surprise other boys start to go to where he and Piggy are standing.
Soon an older boy named Jack comes with a few other boys. They have gathered as a group as a result of his blowing the shell. Because he has he shell he is voted as the person in charge which Jack does not like. It is the first of many conflicts over power between Jack and Ralph.
Piggy comes up with the idea of no one speaks unless they are the one holding the shell. This represents the parliamentary rules of civilization which Piggy tries to retain through-out his life on the island.