If we shoot someone, then we're attacking them. So if we "shoot" someone with words, then we're also attacking them—but with hateful words instead of bullets. Words are often used to belittle, marginalize, and bully people who are different to us.
That's what Angelou's driving at here. In listing all the many injustices that have been done to black people down the centuries, she includes the way in which language has been used as an instrument of racial oppression.
Even to this day, people of color are subjected to racial epithets on a depressingly regular basis. Yet in the angry tone of defiance that characterizes "Still I Rise," Angelou seeks to transcend such hate speech and proudly affirm her identity as an African-American.