In chapter two of the book, Piggy is important into was. First, generally speaking, Piggy has greater insight and foresight than the rest of the boys. In many ways, he represents order and scientific knowledge. This is why he reminds the boys that no one know that they crashed here, which means that their rescue might not come for a very long time. So, they need to be wise in what they do. This is all the most important, because some of the boys are young and need guidance, and more importantly other of the boys are wild and savage.
Second, at the end of the chapter, Piggy is instrumental in getting the fire started. Ralph suggests that the boys start a signal fire. The boys use Piggy's glasses to start this fire. This is significant step, because not only are the boys thinking about a rescue, but it is also bringing order to an island with no adults.
At the beginning of Lord of The Flies, Piggy is very critical and judgmental of the boys. He believes that he is "better" than them in the sense that he is very smart and reads a lot, along with doing well in school. He has a fairly large base of knowledge, while to him, the others boys don't. He is one of the most level headed ones in the beginning, and helps to remind/tell the rest of the boys what is most important and what needs to be done. He helps keep order and even start the fire.