I read the book, but I need to define the theme and a central metaphor in Black Boy.
The main theme of Black Boy is growing up in an hostile environment and eventually escaping it. The protagonist, Richard, the black boy of the title who narrates in the first person the autobiographical story, has to fight not only against the Jim Crow, segregated and racist society of the South, but also against his own race. Richard finds that members of his family are bigoted and hinder his own intellectual development. This has been interpreted, along with some passages of the book, as a negative judgement on African American culture as a whole and critics such as Henry Louis Gates have disapproved of Richard as an individual who wants to emerge at the expense of the community. To these critics, Richard cannot be a representative of his own race, he is the exception, not the rule.
A central metaphor of the work is hunger. The second part of the autobiography, published posthumously is tellingly called American Hunger and recent editions bear both titles Black Boy/American Hunger. To Wright, hunger becomes a concrete part of his existence. It is both literal (lack of food) but also moral/ethical (hunger for justice and knoledge). To escape his dire conditions, Richard fantasizes through books and language (see the long narrative lists that are intervowen into the narrative).