I am the darker brother. (line 2)
This quote sets the stage for the rest of the poem, establishing the speaker as African-American and placing him in a very interesting relationship with his white counterparts. He establishes himself as a "brother." Other than the slang term, what does this do to the tone of the poem? Why do you think he calls himself family in that way?
They send me to eat in the kitchenWhen company comes, (lines 3-4)
This moment sets up the power dynamic between white Americans (the "they") and black Americans in this poem. The white family is sending the speaker (who's either a slave or servant) away to go "eat in the kitchen" because they don't want him to be seen by their guests. (Side note: how does this juxtaposition of family and slavery affect the beginning of this poem? What does it do?)
Tomorrow, I'll be at the table (lines 8-9)
Looking towards the future ("tomorrow" – which, in this case, really means many years in the future), the poem envisions a world in which all races can be at the same table (metaphorically speaking, of course – though, there's a literal element to this, too). The speaker is envisioning a world in which he'll be just as welcome as all the free people in the country.