conch, Piggy is unable to get the attention and respect that holding the shell is supposed to bring.  (This is partly because the fire has caused chaos, and partly because no one takes Piggy seriously.)  Panic ensues, as the little children watch the flames and scream that they are afraid of "snakes."

In chapter two, Ralph holds an assembly to explain to the boys that they are on an uninhabited island and begins to create rules necessary to establish a civilized society. As soon as Ralph mentions that they must build a signal fire, Jack disobeys the conch by enthusiastically telling the boys to follow him up the mountain. The group of boys immediately forget about the assembly and follow Jack to the top of the mountain, where they begin collecting a massive amount of dry wood from the surrounding area. After the boys use Piggy's glasses to light the fire, it grows out of control and creates a minor forest fire. Tragically, the littlun with the mulberry-colored birthmark dies in the forest fire. One could argue that Jack is primarily responsible for the forest fire because he interrupted Ralph's assembly to lead the boys to the top of the mountain, where they enthusiastically gathered too much dry wood. However, each boy contributed to building the massive signal fire, which blazed out of control. Therefore, one could also argue that each boy is somewhat responsible for the forest fire.

To Ralph, keeping the fire ablaze is the only way for the boys to ever be rescued. In addition to serving as a signal to any passing planes or ships, it also cooks the meat brought home by Jack and his hunters. For Jack, this purpose is the main importance of the fire. Partly because Jack has no respect for Ralph after losing the "election" as chief, Jack sees little need for the signal fire to keep blazing. In his mind, it takes time away from the hunt. As for the fire going out in Chapter 2, the boys built the fire too big and it grew out of control, threatening to destroy a good part of the island. In their frenzy, they piled too much wood on the fire which eventually collapsed upon itself. Ralph saw that the fire did not produce enough smoke, signifying that it probably needed to be watched more carefully with small, green brush and wood applied in order to produce better signal smoke.

The boys go to the top of mountain. They gather dried wood and make a huge pile. For kindling, the twins Sam and Eric find dried leaves and pile them on top of the wood. Once this is accomplished, they are unsure of how to start the fire. Jack suggests rubbing two sticks together, and Roger says something about making a bow and spinning the arrow. Finally, when Piggy makes it up the mountain, Ralph asks him if he has any matches. Jack is suddenly struck with the ideas to use Piggy's glasses to make a fire. Jack takes the glasses from Piggy's face and kneels. Ralph takes the glasses and tries to start a fire.

Ralph moved the lenses back and forth...till a glossy white image of the declining sun lay on a peice of rotten wood. Almost at once a thin trickle of smoke rose...and a tiny flame appeared...[it] enveloped a small twig, grew, was enriched with color...[and] the flame flapped higher.

This is significant because if the fire goes out, Piggy is the only person who has the ability to relight it.

In chapter two of Lord of the Flies, by William Golding, Ralph conducts a meeting of all the boys on the island. They discuss many things, but what the littluns are most worried about is the beast, the imagined creatures (presumably snake-like things) about which the boys have been having nightmares. Both Ralph and Jack, the two leaders, try to dispel their fears.

Ralph's way of doing this is to talk about being rescued. He is confident they will be rescued, though he has absolutely no evidence with which to support his belief. In order for that to happen, he says: 

"We can help them to find us. If a ship comes near the island they may not notice us. So we must make smoke on topof the mountain. We must make a fire.”
“A fire! Make a fire!”
At once half the boys were on their feet. Jack clamored among them, the conch forgotten. “Come on! Follow me!”

The boys race to the top of the mountain and amass a great pile of dried sticks, branches, and even logs. It would be a prodigious fire except for one tiny detail they had all overlooked:

Ralph and Jack looked at each other while society paused about them. The shameful knowledge grew in them and they did not know how to begin confession. Ralph spoke first, crimson in the face.
“Will you?”
He cleared his throat and went on. “Will you light the fire?”
Now the absurd situation was open, Jack blushed too. He began to
mutter vaguely.
“You rub two sticks. You rub–”
He glanced at Ralph, who blurted out the last confession of incompetence. “Has anyone got any matches?”

Piggy finally arrives, panting, at the top of the mountain. Ralph immediately asks if Piggy has any matches, but it is Jack who quickly lights on the idea of starting a fire with Piggy's "specs" (glasses). The poor boy is nearly attacked but is willing to let the others start a fire with his glasses, which they do. They use them as a magnifier of the sun to create smoke and then a flame.

Unfortunately, of course, this little rescue fire becomes a conflagration which destroys not only a portion of the island but one of the little boys, as well. Every other fire on the island is started the same way: with Piggy's spectacles. 

The answer to this question can be found about halfway through chapter 2. The boys are meeting together to discuss their situation. The conch is being used, and readers get introduced to the collective fear of the beast, which will continue to grow. Eventually, the arguing about whether or not a beast actually exists switches to the boys wanting two things:

We want to have fun. And we want to be rescued.

The idea of rescue is an important one, and Ralph says that their best chance of rescue is for a passing ship to somehow see that the island has people on it. Ralph states that the best way for this to happen is to have a lot of smoke, and in order to have smoke, the boys need fire.

"There's another thing. We can help them to find us. If a ship comes near the island they may not notice us. So we must make smoke on top of the mountain. We must make a fire."

"A fire! Make a fire!"

At once half the boys were on their feet. Jack clamored among them, the conch forgotten.

The logical reason for a fire is that it helps the boys get rescued. I also believe that the fire idea catches a lot of initial support because they are adolescent boys, and burning stuff is fun.

The boys are meeting together and among other things they discuss the fact that they are alone and that it will be hard for anyone to rescue them. Because it is an island and no one knows where they are, they are worried. Their worries are only intensified when the boy with the mulberry colored birthmark suggests that he saw some kind of snake-like beastie thing in the night that will carry them off and kill them.

They discuss how they will get organized to hunt for meat and then Ralph suggests that they ought to light a big fire in order to have a signal for any nearby ships to find them. The boys are very excited about this and rush off to build a huge fire atop the mountain. Ralph wants to be sure that they will keep the fire going at all times in order to maintain a signal but their big fire burns too hot and doesn't produce smoke so they discuss using greener wood in the future to produce more smoke.

In chapter two, Ralph holds an assembly and explains to the boys that they are on an uninhabited island. Ralph then makes a rule regarding the conch and attempts to quell the hysteria regarding the identity of a beast, which is brought up by the "littlun" with the mulberry-colored birthmark. The last issue Ralph discusses concerns the importance of creating a signal fire on the top of the mountain, where passing ships will be able to spot the rising smoke. Immediately after Ralph mentions that they must build a signal fire, Jack instructs the boys to follow his lead as they completely dismiss the conch and race up the mountain to start the fire. Golding writes,

All at once the crowd swayed toward the island and was gone—following Jack. Even the tiny children went and did their best among the leaves and broken branches. (52).

As the boys are racing up the mountain, Piggy scolds their behavior by commenting that they are acting like a crowd of little kids. Ralph and Piggy then proceed to follow Jack's lead and meet up at the top of the mountain, where they use Piggy's glasses to start a signal fire. Unfortunately, the boys create an uncontrollable conflagration that burns the surrounding side of the mountain.

In chapter 2, the boys run off to get wood for the fire.

After the boys gather to discuss their situation, it becomes clear that there are no adults around to help them.  In order to get rescued, the boys need to make a signal.  They decide they need to make a fire as a smoke signal.

Jack goes off to find wood for the fire, and the other boys follow him before Ralph can stop them.

The space under the palm trees was full of noise and movement. Ralph was on his feet too, shouting for quiet, but no one heard him. All at once the crowd swayed toward the island and was gone–following Jack. (ch 2)

Basically, the boys want to do something, and they find looking for wood interesting.  As long as something is novel and fun, they will do it.  Yet there is not really order and focus.  Ralph is not able to act as a leader, and Jack is only undermining Ralph.

When Ralph, Jack, and Roger return to the beach after visiting the top of the mountain, they frantically explain to the other boys that they also witnessed the beast. Piggy is perplexed at the boys' terrible news, and Jack suggests that his hunters may be able to kill the beast, which is an idea that Ralph finds preposterous. After Jack holds an assembly, where he attempts to usurp power, he runs off to the other side of the island and exits Ralph's group. Piggy then suggests that they build a new signal fire on the beach, and the boys happily begin collecting firewood from the surrounding area. Being rescued is still Piggy's and Ralph's main concern, which is why they decide to build another signal fire on the beach. Unlike Jack and his hunters, they understand the importance of a signal fire and are not about to abandon hope. They also fear the beast on the top of the mountain and believe that the beach is the second-best location for a new signal fire. After gathering a large amount of firewood, Ralph and Piggy notice that the majority of the boys have left the beach and followed Jack to the other side of the island.