The above editor is correct: the information you need is in chapter four of the novel, rather than in chapter two.
If you need evidence for your answer, it begins on page 75 of my edition. The entire chapter takes place in Crooks' room, which is adjacent to the barn and is entered through the barn. When Lennie appears and explains that he saw Crooks' light on, so he came in, Crooks says:
"Well, I got a right to have a light. You go on get outta my room. I ain't wanted in the bunk house, and you ain't wanted in my room."
"Why ain't you wanted?" Lennie asked.
"'Cause I'm black. They play cards in there, but I can't play because I'm black. They say I stink. Well, I tell you, you all of you stink to me."
Crooks isn't allowed in the bunk house, because of segregation. The races are kept apart. The reader assumes that the idea of Crooks stinking is a stereotypical idea the whites project upon him due to their prejudices. They don't want him in the bunk house because he is black.