This passage from William Golding's Lord of the Flies occurs at the end of chapter three. Simon has been working on the shelters with Ralph all day; however, when he has a chance to get away, he does. The littluns follow him at first, knowing he is patient and they can ask him to pick some fruit for them, since all the fruit is too high for them to reach.

Finally Simon is able to leave, and he makes his way to the spot described in the passage you mention. When he arrives, Simon looks around to be sure no one is watching him before slipping into his private sanctuary. That is the only significant action in this passage; the rest is pure description.

There are three notable details about this passage and this sanctuary. First, it is isolated and Simon does not want to share it with anyone else. Golding describes the foliage as a "canopy," and very little light is able to penetrate Simon's hiding spot. Simon needs time alone because he is the embodiment of man's spirit which sometimes needs solitude in order to rejuvenate.

Second, it is a familiar place to Simon. He does not have to grope around and wonder where to find "the mat" which is what Golding calls the opening flap for this secret spot. Simon has been here before.

Finally, we (the readers) have also been to this spot before. In chapter one, Jack, Ralph, and Simon explore the mountain, and they find a bush with candle buds. (Candle buds are not everywhere, or this particular bush would not have captured the boys' attention.) Ralph and Jack are spectacularly unimpressed with the find. Jack is disgusted because the candle buds are not edible, and Ralph displays a stunning lack of imagination when he remarks that, though they look like candles, they cannot be lit. 

Simon is the one who is moved by the sight of the candle buds. He says, “Like candles. Candle bushes. Candle buds.” He immediately appreciates their resemblance to candles, a figurative representation of the light (truth) he will try to give the others. 

Simon visits this place again where he encounters the pig's head on a stick, the Lord of the Flies. His place of tranquility is ruined by the evil truth about the nature of man, and soon Simon will be killed by the reality of that evil nature.