The boys who appear out of the jungle are those boys who were on the plane when it crashed. They have all been separated in various directions. When Ralph blows the conch, the boys hear the noise and are attracted by it. In fact, Jack thinks he hears a trumpet. The boys gather around Ralph and Piggy and thus Ralph is able to begin organizing the group and planning what they all should do.
Your question is difficult to answer without a more direct indication of what part of the book you are referring to. If you are referring to the very beginning of the book, then the boys who first appear out of the jungle are Ralph and Piggy, who begin exploring at once, Ralph excitedly and Piggy cautiously. They proceed to have a dialogue about the island and we learn of Piggy's unfortunate nickname for the first time.
Be sure to ask more specific questions in the future. Refer to specific chapters or characters. Good luck!