How did Ralph call the first meeting? Why did he do this?

After the plane crash, Ralph begins to look around by climbing down rocks to get to the beach. Once there, he goes near a lagoon on the beach where he encounters a chubby boy named Piggy. Piggy sees a conch sea shell that can be used to make a large, trumpetlike sound which anyone on the island might hear. Ralph blows on the conch; the boys that survived the plane crash come toward the sound and begin to assemble with Ralph and Piggy.