In Chapter One of Lord of the Flies, Ralph discovers a creamy shell laying among the ferny weeds, which Piggy informs him is a conch. Piggy recalls that he's seen this kind of shell before on the back wall of a friend, claiming, "He used to blow it and then his mum would come. It's ever so valuable."
Piggy rambles on about the great value of the conch and what kind of sound it makes while Ralph carefully examines it. Piggy then makes the suggestion that the boys could use the conch to call the others to have a meeting, thinking that this must have been the reason why Ralph plucked the shell from the water. Piggy teaches Ralph how to blow the conch, recalling that his friend "kind of spat" to make the noise. Ralph tests it out, and a "deep, harsh note" is emitted, frightening the nearby animals and causing other boys to arrive on the scene.
Piggy has prior experience with conchs as his Aunt had one and she taught him how to blow it. Piggy, in turn, teaches Ralph how to blow the conch, and from that moment on it is used to keep the peace and order among the boys on the island until Jack declares it is no longer needed.