The Cunningham's were poor white people in the city of Maycomb. They were proud people. The first we see of them is when Scout is in class, and Walter does not have his lunch. She tries to explain to Miss Caroline that he is a Cunningham. She says to the reader,
"He didn't forget his lunch, he didn't have any. He had none today nor would he have any tomorrow or the next day. He had probably never seen three quarters together at the same time in his life." (pg 20)
Walter's father was one of Atticus's clients. Mr. Cunningham was never able to pay Atticus for his fees, so he did things for him to pay off his bill. For example, he left a load of stovewood in the back yard, and he gave them a sack of hickory nuts, turnip greens, and holly. When Scout asks why he pays Atticus that way, Atticus tells her,
"Because that's the only way he can pay me. He has no money." (pg 21)
They were proud people, and they taught that to their children. Scout even knows that,
"The Cunninghams never took anything they can't pay back ---no church baskets and no scrip stamps. They never took anything off of anybody, they get along on what they have. They don't have much, but they get along on it." (pg 20)
Walter has not passed the first grade, but he explains to Atticus that,
"'Reason I can't pass first grade, Mr. Finch, is I've had to stay out every' spring an' help Papa with the choppin' but there's another'n at the house now that's field size..'" (pg 24)
Yet, he could talk fields and crops like a man with Atticus. They were poor white folks, but they were respected unlike the Ewell's. They are in direct contrast to the Ewell's. The Cunningham's work hard and do not take handouts. The Ewell's take handouts and do not work hard.
The Cunninghams are regarded as the "royal poor" because they are proud of what they have. They don't accept anything from people, if they can't return it. They are poor country folks and we learn about the Cunninghams through (mainly) Walter Cunnigham. For example, Walter refused to take a quarter from Miss Caroline because he could return it back to her. Although they are looked down on, they are proud and have dignity.
Hope this helped :)