In the exposition, Lennie and George are introduced as two migrant workers coming down from weed where they were working. The story is foreshadowed entirely within this section. They get to their camp, talk about the American Dream, and then Lennie kills it or in this case kills a mouse.
During the rising action, the story is continued to be foreshadowed and tension starts to build between George, Lennie, and the other workers. The rest of the characters are introduced here, including Curley who is the main antagonist of the story. During this section Candy's dog is also killed by Carlson, which foreshadows the end of the book. Candy, George, and Lennie also talk about saving up money to buy their American Dream and promise to keep it secret from the other workers on the farm.
The climax of the story begins with Lennie beating up Curley, and the farm workers heading off to town. George tries to keep the plot for their American Dream secret during this time but fails due to Lennie and Candy talking about it to Crooks and Curley's Wife. This section is ended with Lennie in the barn with the puppies. This section further foreshadows Lennie's death and George being the one to kill him.
During the falling action, Lennie ends up killing the puppy and Curley's wife walks in to talk to him. He talks to her for a while and she spills everything about her past and marriage with Curley. Lennie explains about his aunt and his obsession with soft things, and she exploits this by letting him touch her hair. He then kills her and thus sets off the series of events leading to George killing him.
During the Resolution Lennie spends his time hiding where George told him to. As a result of Lennie killing Curley's wife the farm workers set out to kill Lennie and George is with them. After George learns of the news he knows he will have to kill Lennie, and this is where he gives up on his American Dream. Lennie experiences hallucinations during the climax showing that he is aware of his burden on George, while George searches for him with the farm members. George finally confronts Lennie and puts him in a dreamlike state where he imagines his American Dream and then finally kills him. Steinback then shows how little this matters by having George walk off and just leave Lennie laying in the sand.