Although Ralph is the one who first sees the conch, he has no idea it can be used as a trumpet. In chapter 1 Piggy and Ralph meet at the swimming lagoon, and Ralph spies and frees the conch, an 18-inch shell. Piggy becomes very excited because he has seen a similar shell before. The person who had it on his back wall blew into it and it "mooed like a cow." Piggy then realizes they could use the conch to call the others. In typical ingratiating fashion, he attributes his brilliant idea to Ralph, saying, "That was what you meant, didn't you? That's why you got the conch out of the water?" Ralph doesn't deny it; he lets Piggy credit him for Piggy's idea. Piggy then instructs Ralph on how to blow into the conch to make it reverberate. It requires a certain lip and tongue action as well as a deep diaphragmatic exhale. Piggy himself is unable to blow the conch because of his asthma. This foreshadows the relationship of Piggy to Ralph, Piggy being the "brains behind the throne." Later, in chapter 2, Ralph is declared chief because he has possession of the impressive conch, and he creates the rule that at meetings one must have the conch in order to speak.
Ralph uses the conch shell in two ways. First, he uses it as a signal for others to gather for a reason. When he blows it like a horn, other boys come running and and assemble themselves together. Secondly, once the meeting begins, whoever holds the conch shell is permitted to speak. This ensures that meetings are conducted in an orderly fashion, and that everyone gets a chance to speak their piece without fear of interruption.
Piggy seconds the use of the conch shell for order, as he is overly concerned with having a list of who is on the island, as well as knowing what everyone's doing. Ralph, the designated chief during the first part of the novel, tries to allow everyone to have a say, so the conch shell allows him to do just this, without having to yell and use his authority too often.