Black Boy is Richard Wright's memoir and narrates his experience of growing up poor and black in the American South.
Wright's father left when he was young, requiring his mother to struggle to earn enough money to keep her and Wright housed and fed. For most of Wright's young life, he was moved around across the South to stay with different family members when his mother didn't have enough money to provide for them.
In each of his various experiences in the South, Wright had encounters with white people that slowly revealed to him that he was the subject of incredible repression in the form of racial discrimination. He also realized that, even though he believed it was wrong, this racial discrimination had damaging effects on his sense of self. This realization--that the black person in America is suffering internally from the degrading effects of discrimination--is the defining realization of his bildungsroman and the main idea of his memoir.
The passage below is a helpful example of the way Wright figures the impact of discrimination:
"The fact of the separation of white and black was clear to me; it was its effect upon the personalities of people that stumped and dismayed me. I did not feel that I was a threat to anybody; yet, as soon as I had grown old enough to think I had learned that my entire personality, my aspirations had long ago been discounted.... And when I contemplated the area of No Man's Land into which the Negro mind in America had been shunted I wondered if there had ever existed in all human history a more corroding and devastating attack upon the personalities of men than the idea of racial discrimination."