This is a good question. Let me give you a few examples of the symbolism of the conch.
First, at the beginning of the novel Ralph and Piggy find the conch and it is used to bring the boy together. The very fact that they have come together shows civility and organization. This is an assembly of sorts.
Second, when the boys come together for meetings. It is the one who holds the conch that has the right to speak. This also shows civility and order. To take one more step, one can argue that the conch represents legitimate power and democratic principles.
But as the story progresses, the conch is destroyed (along with Piggy), and this is a symbol that civility is now gone. There is something to this interpretation, because after this there is general mayhem and the sheer lack of order and civility.
In Lord of the Flies, symbolism is very important in understanding William Golding's message that human beings have been conditioned to live according to rules. Without the structure of rules, Golding contends that they will adopt a basic and even savage existence, much like a wild animal, where survival and self-preservation are far more important than community, co-operation, collective safety and fairness.
The conch is the first noticeable symbol on the island and the fact that Ralph spots it first and Piggy recognizes its value and how they can use it is very significant. At first, it is for the purposes of calling the other boys and having a meeting as that is what makes most sense to Piggy. The fact that Piggy walks among the boys taking their names and that the boys "gave him the same simple obedience" (ch 1) reveals how naturally it comes to all the boys to follow a structure even in their obvious confusion. They act according to the expectations of adults and in Piggy's case of his auntie, in particular. As time goes on and the hope of rescue and a return to that civil society they initially strive for diminishes, so too does the conch's influence.
Even Jack and his choir boys have a very defined structure and follow the sound of the conch under Jack's leadership. The choir boys follow Jack's orders and are "wearily obedient" (ch 1). The boys' decision to vote for chief also reveals their conditioned behavior and the fact that Jack is "chapter chorister and head boy" and so should be a firm believer in the power of the conch yet becomes one of the most savage of all, seems to confirm Golding's theory.
After Ralph has been voted as chief, it is the conch that reminds the boys of his authority and how the conch must be respected. However, even as early as the third chapter, Ralph is complaining that the boys "work for five minutes then wander off..." suggesting that the conch may call order but no one actually follows instructions. The "littluns" fall into their own routine which includes obeying "the summons of the conch" which they see as "a link with the adult world of authority" (ch 4) but Ralph is becoming overwhelmed by "the wearisomeness of this life" (ch 5) and is changing his understanding of the role of the conch for which he has "a kind of affectionate reverence." Ralph recognizes the almost hypnotic influence of the conch and uses it to calm any disturbance although he has realized that promises made are rarely kept.
Jack is changing and once he has painted his face he feels "liberated from shame and self-consciousness" and so the conch will not deter him. In fact, Jack comes to consider the presence of the conch as a challenge to his own authority and, when it is destroyed it is as if he has been released from that hypnotic spell. Rather than lamenting Piggy's death, he feels triumphant that the conch can no longer have any authority.