This is a very broad question, and so you are going to receive a very broad answer. If you want more details about some of the ideas in this brilliant play, please follow the links below, that will take you to the enotes study guide section of this play.
Just to give you a few ideas, however, you can't possibly hope to examine this play without thinking about dreams. The central characters have to cope with the tension that is created between their dreams and what they hope to do with their lives and the series of oppressive facts that threaten to prevent them from achieving those dreams. Beneatha for example wishes to study and become a doctor in spite of being a black woman and being poor. Let us remember that the title of the play is an explicit link to the theme of dreams, as it refers to a poem by Langston Hughes where he talks about dreams that are deferred or forgotten about. He ponders whether such dreams actually become "like a raisin in the sun." Each person in the Younger family has their own dream, and their emotions are clearly linked to their success or inability to achieve those dreams. At the end of the play, it is the dream of having a house that unites the family and that they realise is the most important dream. It is the unity that this shared dream gives the Younger family that allows Walter to stand up to Lindner and to cope with his recent failure of losing the rest of the insurance money, ironically allowing himself to show himself to be a man after he has failed to act like one. Note with what confidence he stands up to Lindner:
And we have decieded to move into our house because my father--my father--he earned it for us brick by brick. We don't want to make no trouble for nobody or fight no causes, and we will try to be good neighbours. And that's all we got to say about that. We don't want your money.
Pursuing this dream as a family is something that bestows dignity and hope on each member of the Younger family, but perhaps epecially on Walter as he finally becomes the man of the household and follows in his father's footsteps.