The structure and form of "Mother to Son" by Langston Hughes is free verse.
In the poem, the narrator is a mother offering advice to her son. To explain her life journey, she uses the metaphor of a stairway. As she keeps climbing, she often encounters rough spots, but she does not give up. She encourages him to follow her example, to remain determined, and to keep going and not stop and rest.
Concerning structure and form, the poem has one stanza of twenty lines. The poem is written in free verse, which means that the lines are of varying lengths and there is no unifying rhyme scheme or metrical pattern.
Instead of a formal rhythmic structure, Hughes allows the elements of the metaphor and his careful choice of words to lend cadence to the poem. We see this cadence as the narrator begins to describe the stairway she has undertaken through life. Each line describes one difficulty that is rendered into language fitting the metaphor: "tacks," "splinters," "boards torn up," "no carpet on the floor," and "bare." After this, each line describes one determined action that the narrator has taken to strive forward: "a-climbin' on," "reachin' landin's," "turnin' corners," and "goin' in the dark."
The vernacular that the narrator uses adds to our awareness that this is an African American woman who has led a difficult life full of hardships. She knows that her son's life will not be easy, either, and she wants to prepare him for it as best she can.
We see, then, that though Hughes uses free verse in this poem, he has structured it very carefully to fit the metaphor he has chosen and to bring out the voice and character of the narrator.