Beneatha says, "Enough of this assimilationist junk!" She means she's tired of people pressuring African-Americans to abandon their cultural identity and act more like white people.
Walter joins Beneatha's performance because it lets him forget his problems for a while and feel connected to his African roots.
Ruth is worried and disappointed in Walter that evening. She feels he's worn out and frustrated with their life.
Walter imagines himself as a great warrior to escape his feelings of failure and powerlessness. It helps him feel strong and respected.
George Murchison looks down on Walter and finds Beneatha's interest in African heritage odd. He's not interested in his African roots because he's more focused on fitting into mainstream American society.
"Eccentric" means unusual or quirky. George thinks Beneatha's curiosity about her heritage is eccentric because he doesn't understand why she cares so much. Whether you agree depends on whether you think exploring cultural roots is important or not.
George turning down Ruth's offer of a beer shows the class difference between them. He sees himself as more refined and wants to distance himself from working-class habits.
Walter and Mama's relationship is tense. Mama acts distant because she's disappointed in Walter's choices and wants him to be more responsible.
Ruth asks about sunlight to see if there's hope for a better future. Sunlight symbolizes hope and a fresh start for her.