As the boys are stranded on an undeveloped jungle island, there are of course a lot of descriptions of natural features and details throughout the novel. It would be impossible to cover them all, but some things you could focus on:
1. When the boys first crash land, some of them express a kind of happiness or joy at their predicament. For example, Ralph does handstands to show how carefree he is. Jack seems to be excited for the prospect of hunting. In these early days, Golding describes the island as a kind of paradise. You can imagine it as a kind of place you would pay a lot of money to go for your holiday. But at the same time, the writer includes clues that the island is not the paradise it seems. You can look for mention of Ralph's "snake-clasp" belt or the plants that look like skulls.
2. Some of the things that one finds in nature become very important parts of the boys' lives. The wild pigs become a fixation of Jack's. His hunt for them when he crawls along the jungle floor sniffing at their steamy droppings shows just how far and how fast the boys have come. Another natural detail you might want to focus on is rocks. There is the rock that the boys push down the hill in chapter 1, there are the rocks they throw at each other in a kind of violent play, and there is the rock that kills Piggy and destroys the conch. Fire would be another natural motif you could examine.