A conch is a spiral-shaped sea shell that can be used as a horn. The first chapter is titled "The Sound of the Shell" because of the significance of the conch. Piggy, the most intelligent of the boys, recognizes it is a conch and that it can be used to summon the other boys to a meeting. Since Piggy has asthma, Ralph tries to get a sound out of the conch. After a few tries, he gets the desired effect: 

A deep, harsh note boomed under the palms, spread through the intricacies of the forest and echoed back from the pink granite of the mountain. 

Ralph continues with the conch and the boys gradually gravitate to him and Piggy. The conch is used to organize the boys. The conch establishes order. Although some of the boys think Jack should be chief, Ralph's calming manner and the fact that he is holding the conch illustrate the presence of a leader. Ralph holds the conch up and commands attention. At their meetings, he who holds the conch will be allowed to speak and be heard. The conch is an important tool in keeping the boys organized and civilized. It is therefore an important symbol of order in the novel. As the boys become more savage, the power and significance of the conch decreases.