He frequently uses metaphors, similes and symbolism. If you look at his poem "Mother to Son," he has a mother giving advice to her son, and she compares life to an old staircase that one must keep on climbing your entire life. She says to her son,
"Life for me ain't been no crystal stair./It's had tacks in it,/And splinters,/And boards torn up,/And places with no carpet on the floor—/Bare./But all the time /I'se been/a-climbin"
So, here, Hughes uses a metaphor, comparing life to a worn out and treachorous flight of stairs that one must climb up. In his poem "I Too, Am America," Hughes uses symbolism. He states that "Tomorrow I'll be at the table when company comes." The table is a symbol of equality. Black people were forced to eat in a separate room from the whites, and he is using sitting at a table with the white people as a symbol for the equality that he feels will come to him and his people eventually.
An example of similies is in the poem "Harlem". He wonders what happens to dreams that are never lived or realized. He asks, if it dries up "like a raisin in the sun," or does it "fester like a sore" or "stink like rotten meat" or crust over "like a syrupy sweet"? All of those are similes for what he imagines happens to those dreams that we never have the chance or courage to act upon.
I hope those examples help a bit; Hughes uses all sorts of literary devices, but metaphor, symbolism and similes can be seen in those three poems. Good luck!