How do all the boys know where to gather when the conch shell is blown?

When Piggy finds the conch in chapter 1, Ralph is drawn to the shape and appearance of the shell. Piggy excitedly rambles about his knowledge of conch shells, and then he says to Ralph, "We can use this to call the others. Have a meeting. They'll come when they hear us," and Ralph understands that this is why Piggy went to the effort of getting the conch out of the water in the first place. Ralph tries blowing on the conch, and the sound scares birds into flight, so he blows on the conch a few more times to see what will happen. When the boys start to emerge from among the palms, Piggy and Ralph realize the power of the conch. During this first gathering, the boys summoned by the trumpeting of the conch discuss Ralph's role as chief. The sound of the conch is what guides the boys and tells them where to gather.