And let that page come out of you— Then, it will be true. (4-5)
This, the teacher's assignment, sets up the whole poem to be about finding the truth in one's own self. If something comes out of you—is truly part of your identity—then it will be "true," this assignment posits. Now of course someone could sit there writing "blah, blah, blah," and that probably would come out of them, but it wouldn't have much insight or truth in it. So it's up to our speaker to determine how successful the speaker's assignment will be for him.
I am twenty-two, colored, born in Winston-Salem. (7)
This is the first line in which the speaker is writing about himself. So it's likely the most basic, integral part of his identity. He's young, black, and born in the south. Given the date this poem was published—1951—we know that it's likely that, as the speaker guessed in line 6, the assignment would not be as simple for him as for a white person his same age.
[…] But I guess I'm what I feel and see and hear, Harlem, I hear you: hear you, hear me--we two--you, me, talk on this page. (17-19)
Though we know that our speaker was born and brought up in the South, here, we hear about how living in Harlem affects his identity. He feels as if he converses with the city—there's plenty to see and hear and feel in New York. But it's not one-way. As he's affected by the city, the city is affected by him. His experience of Harlem is different from the experience that anyone else could have in Harlem. And that's part of his identity.
[…] Me--who? (20)
If you had to sum up the whole theme of identity in two words, these two would likely do the trick. Throughout the whole poem the speaker is trying to answer the question he puts forth in these lines: "Who am I?" Except he's got a slangy conversational rhythm going on, so "me—who?" comes along and shortens the question up even more. In this form, we're able to see the frustration and confusion, the frantic feeling that can sometimes come along with searching for an answer to this question.
Well, I like to eat, sleep, drink, and be in love. (21)
That's a pretty simple way to sum up most people. This line comes at the beginning of a few more that name specific things the speaker likes, but the point here is that, as unique and different as people are from each other, at the end of the day our identities give us a lot in common.
You are white-- yet a part of me, as I am a part of you. That's American. (33)
Here, the "you" could be the speaker's instructor, or anyone who's reading this poem, even. Throughout the poem, the speaker has been debating how being black makes him different, or not, from white people. Here, he's starting to come to terms with the relationship between the two races. They may have their differences, but they're a part of each other, in America. It's interesting to think back to 1950, when this poem was written, and then think forward to today, and look at how the relationship between the two races has changed, and how it hasn't.