How does the "African" scene show a new side to the relationship between Walter and Beneatha?

The scene, which takes place at the beginning of Act Two, Scene One, does not exactly "show a new side" to their relationship, but instead is a moment at which both are able to connect to each other through a desire to tap into the glory of their ancestors. Beneatha wishes to do this so that she can forge a new sense of identity and kinship based on a black aesthetic. Walter "channels the ancestors" out of a desire to feel greater pride in himself as a man.

Beneatha, through her education and contact with African exchange students, is learning more about Africa, including its rituals, customs, and art. Though her intentions are good, she is not as attuned to the continent as she thinks, a fact that is revealed in the exposition of the play:

She parades for RUTH, her hair completely hidden by the headdress; she is coquettishly fanning herself with an ornate oriental fan, mistakenly more like Butterfly [McQueen, "Prissy" in Gone with the Wind] than any Nigerian ever was...She promenades to the radio and, with an arrogant flourish, turns off the good loud blues that is playing...

"Enough of this assimilationist junk!" she asserts, without realizing that blues is as uniquely and distinctly a product of black expression as the costume her boyfriend, Asagai, bought her. Her behavior comes off as less regal than intended and should remind the audience more of Butterfly McQueen's performance as the servile "Prissy" in Gone with the Wind. Lorraine Hansberry does not draw this parallel to insult Beneatha or the memory of Ms. McQueen, but instead uses it to show that Beneatha is trying to usurp something that is, in fact, foreign to her. She is no more a product of Nigeria than Asagai would be a product of Kenya. She has African ancestry, yes; but she is not culturally African.

While Beneatha parades around, Walter stumbles in drunk. It is important that this scene begins after he has left the apartment in shame due to being unfavorable toward Ruth's pregnancy. He does not want the pregnancy because they can barely afford the child they have. Another, in his estimation, would make it even more difficult for them to improve their lives.

By channeling African imagery (e.g., "the lion is waking," "waters rushing against the shores of the coastlands," "the birds flying low over the mountains and the low places of our land"), he can feel the majesty, power, and strength of the man he wants to be. He does not feel this as a lowly Chicago chauffeur living in a housing project on the Southside.

What both Walter and Beneatha are trying to do is to forge identities as black people that are separate from—and more positive than—what America has taught them they are. They are trying to learn to have pride in themselves. In this regard, the two share a common goal.