Fairly early in The Lord of the Flies, a conflict develops between two potential leaders among the schoolboys stranded on the island. First, there is Ralph, who (broadly) represents pragmatism. He's a natural leader, but it's obvious as he faces challenges that he has his indecisive moments. He wants the boys to build huts and work together to take care of the litt'luns and the fire (for rescue, but also for hope).
Then there is Jack, who is more action oriented. He represents a "leap before you look" philosophy, and he thinks that by killing a pig, he will unify the boys and find food.
In the chapter "Painted Faces and Long Hair," the boys begin their descent into savagery, and this is foreshadowed in the chapter's title. Jack leads them in face-painting in preparation for killing a wild pig they know lives on the island. Ralph, meanwhile, is trying to talk the boys into building huts. Ralph is also making sure there is plenty of kindling for their fire and that the fire stays lit.
But the face-painting distracts the boys who are supposed to watch the fire. Ralph discovers that although kindling is available, the fire has died out. The fire represents a possible signal, and it's also a way to cook the pig! Mainly, though, the lack of fire is a symbolic representation of their tentative loss of civilization.