The boys are British schoolboys who have been stranded on the island with no adults because there is a war on and their plane was shot down.
The “boy with fair hair” is Ralph and the “fat boy” is Piggy. Later they are joined by Jack, the leader of the choir, and several other boys including Roger, Simon, Sam’n’eric and the “littluns,” the youngest boys.
Ralph and Piggy are the first ones we see. Soon, more and more boys appear.
The sand, trembling beneath the heat haze, concealed many figures in its miles of length; boys were making their way toward the platform through the hot, dumb sand. Three small children… appeared from startlingly close at hand, where they had been gorging fruit in the forest. (ch 1)
There are no adults on the island. Soon the boys vote to have Ralph be their chief, even though he has no leadership experience. Jack, who does, is annoyed by this.
The boys have been left to thier own devices by the plane crash. They have to fend for themselves, organize themselves, find food and make shelter. It is challenging to keep all of the boys in check, and Ralph proves somewhat unequal to the challenge.