Instead of George and Lennie going to the place their supposed to work, the author makes them stay and camp out at a spot they found about a half a mile away from the ranch. They collected sticks and made a fire so they could make their beans warm. They also talked about their dream and how they are going to make it come true one day. This is significant because we didn't know of the dream until now.
George is sitting at the table playing solitaire when Slim walks up and starts talking to him about what happened and how he ended up on that ranch. George is telling Slim what happened to him and Lennie in Weed because of what Curley's wife was wearing that day. This is significant because Curley's wife is wearing a red dress and it is a symbol for something along with everything else that is red in the book.
In this scene a lot of significant things happen. One of them is the puppy that Lennie petted too hard and killed. The dog means something because that is one of the reasons Lennie left the ranch and went to wait for George at another place. The other significant thing that happened in this chapter is Curley's wife tries and talks to Lennie, and Lennie eventually ends up accidentally strangling Curley's wife to death and leaves her there.
This is one of the most significant scenes in the novel. This is one of the most important because This is where George has to give up his best friend and his dream. By shooting Lennie in the back of the head, because he knew if the others within the ranch got ahold of him, it would be much worse. George had to give up everything and give up his dream even though he knew in the back of his head the dream wouldnt work anyways.