Your question is a little bit vague but here are some possible answers to this question about the things that Ralph and / or Jack had only previously heard about.
In Lord of The Flies, a group of English schoolboys is stranded on an apparently deserted island from where they can only hope to be rescued. The conch, which becomes a symbol of democracy and the right to speak, calls the boys together and Ralph is voted as chief because there are no "grown-ups" to guide them and so the boys have to devise their own organizational structure.
1. When Ralph and Piggy first meet, they do not realize the full impact of what has happened. Ralph is confident that his father will come and rescue them until Piggy tells him that there will be no-one to report where they are because he overheard the pilot talking "about the atom bomb" while the boys were still on the plane. He tells Ralph, "They're all dead" (chapter 1). There is only talk about what may have happened to the plane they were on and in chapter 2, it is Ralph who tells everyone that the plane "was shot down in flames" although he is only talking about what he has heard, not seen.
2. In chapter 1, after the boys have assembled, Ralph, Simon and Jack go exploring to establish if they are on an island. They are overawed at the expanse of the island, and it's "all ours." As they are walking back on the edge of the dense forest, they come across a piglet but it gets away before Jack has the nerve to use his knife to kill it. The boys then discuss the best way to kill a pig which is something they had only previously heard about. Ralph suggests that "you should stick a pig" - from what he has heard and Jack says that it is necessary to "cut a pig's throat to let the blood out." Up until this point, they have only heard about the process, or the reality of killing a pig. They have never actually tried it.
3. When the boys decide to build a signal fire, it is only once the wood is stacked that both Ralph and Jack realize that they don't know how to start a fire and an "absurd situation" is created and they are both extremely embarrassed. Jack has heard that you rub two sticks together to make fire and also realizes that they may be able to use Piggy's glasses as "burning glasses." Ralph supports Jack and helps him by moving the glasses back and forth. Jack blows gently and there is a "tiny flame." The boys had only heard about this process before and, although they are able to create flame, the fire will not be all that they had expected it to be.
4. When the littleun goes missing, nobody knows what may have become of him. The possibility in terms of him having died when the fire was out of control is at the back of everyone's minds but it is not spoken of further.
5. In chapter 6, Sameneric claim that they have seen the beast and this prompts Ralph and Jack to try to find it. Up until now, it has been speculation about snake-like things, beasties and ghosts. At the beginning of chapter 8, Ralph and Jack are convinced that they have now seen he beast itself.
I hope these instances help.