One of the prominent metaphors in Angelou's "I Know Why the Caged Bird Sings" is Maya's recollection of her personal history from "the perch of age." (See pg 5, Ch 4).
This metaphor lets us know that the older Maya is viewing her life with the near-omniscient perspective of being both above and removed from the immediacy of her childhood. Speaking of the well-to-do African-American man who lived next to the Store, young Maya is in awe of "the only colored man I knew...who wore matching pants and jackets."
The older Maya speaks metaphorically of the man as she recounts, "I watched him with the excitement of expecting him to do anything at any time. I never tired of this, or became disappointed or disenchanted with him, although from the perch of age, I see him now as a very simple and uninteresting man...".
Another metaphor can be found in the first paragraph of Chapter 7. Maya and Bailey have just met their father. One feels the child's confusion as Maya describes her world that has suddenly become "humpty-dumptied, never to be put back together again."
A simile (one of many) can be found near the end of Chapter 6, when Maya describes the verbose preacher, Elder Thomas, whose lips she describes as "flapping loose like elastic."