How does Steinbeck present American society through his presentation of ranch life?

Steinbeck primarily presents the "view from below" on the ranch, meaning how life in American society looks to those at the bottom rungs. He focuses primarily on the ranch hands, though we could also add to the mix Curley's wife, a teenage girl without real power. What Steinbeck shows is that life was uncertain, rough, and sometimes frightening for the poorer classes. 

The bunk house where the ranch hands live lacks privacy and the men get very little space to call their own. Instead of a dresser, they each have a crate of two shelves nailed to the wall for personal belongings, and they sleep in bunkbeds in one room. Part of what George dreams of when he envisions having his own small farm is the power to invite--and exclude--whomever he wants. 

George and Lennie's dream of their farm reveals the simple things they lack in their lives, such as the ability not to work an 11-hour day or the chance to take a day off if they need to or want to. It speaks to their deep yearning to put down roots in one spot--to have a real home--rather than wandering from job to job, constantly ending up in new places where they have to learn how to fit in. It also speaks to their yearning for dignity.

George and Lennie have to be careful not to be fired and must grovel in front of the boss. When they raise suspicion in the dog-eat-dog, every-man-for-himself world they live in because it becomes evident they take care of each other, the are expected to answer questions:

The boss deliberately put the little book in his pocket. He hooked his thumbs in his belt and squinted one eye nearly closed. “Say—what you sellin’?”

“Huh?”

“I said what stake you got in this guy? You takin’ his pay away from him?”

“No, ‘course I ain’t. Why ya think I’m sellin’ him out?”

“Well, I never seen one guy take so much trouble for another guy. I just like to know what your interest is.”

Crooks, the black ranch hand, is forced to grovel to Curley's young wife when she threatens to make accusations that could get him lynched. He would like to enter into George's dream of owning a farm, but life has been hard enough on him as black man that he doesn't even let himself dream. 

And although Curley's wife has some power, it is very little. She is a teenage girl without much education, isolated as the only woman on the ranch. 

Life is hard on the ranch hands and Steinbeck hoped that depicting it would raise sympathy that would lead to better conditions for them.