You can find the answers to all of your questions here by visiting the link below to the pages here at eNotes. Just go to the "Navigation" bar on the right, and click any catagory that you are interested in. But here is a brief overview:
The plot revolves around the lives of the Younger family who are about to recieve a large check ($10,000) in life insurance money. The family's patriarch has just died. Each member of the family has ideas about how the money should be spent. The characters argue about the right way to do this, each believing their idea is the best.
The major conflict of Hansberry's play is the struggles of the African-American Younger family, who must battle against poverty and prejudice in mid-20th century South Side Chicago (approx. 1950). Though each family member's story, we learn how poverty and prejudice impacts their individual lives.
An example of dramatic irony can be found as Act I concludes. The protagonist, Ruth, is singing a song called "No Ways Tired" when in fact she is exhausted. She is also experiencing the fatigue that comes in the first trimester of pregnancy, which, of course, will lead to even more conflict.
The main characters are Ruth Younger, the pregnant daughter, who worries that her unborn child will just add more financial hardships to her already burdened family; Walter, the male protagonist, who wants to invest the money in a liquor store, and Beneathea, who dreams of becoming a doctor.