In the novel's setting, 1930s Maycomb Alabama, segregation was standard practice, we can see this with the Finches family cook Calpurnia. In chapter 12 Calpurnia takes Jem and Scout to a black church, there were black churches because blacks weren't allowed to go to any white churches, this is because of segregation. Another example would be when Aunt Alexandra moved in with the Finches as she disrespectfully ordered Calpurnia to carry her luggage to her room as she most likely figured that Calpurnia was nothing more than a paid for service, because all colored people fell below even the most deadbeat white person.
Last but definitely not least we have financial status based social inequality. The Ewell family is a broke family who dwell behind the town garbage dump, in a tin-roofed cabin, they are generally thought of as lower than everybody else because of their financial status. Then we also have the Cunninghams, a very poor yet proud farming family, in chapter three Walter Cunningham is over at the Finches house and Scout says to Calpurnia “He ain’t company Cal, he’s just a Cunningham” she said this implying that he is of a lower class and doesn’t have to be treated