Langston Hughs was a black poet who wrote about black issues of his life and times. He wrote in the 1920's and died in 1967.
Part 1: He talks about his youth. All young people have dreams and aspirations. He was no different. At the time he is writing this poem, he almost forgot about that youthful dream he had when he was young. But when he was young, it was a strong dream, a real dream, and he saw hope as bright as the sun in it.
Part 2: But then reality hit. Obstacles were placed between him and his dream. Slowly, but suddenly it was a wall, a huge wall that rose to the sky. It was because he was black. These obstacles, or the wall, created a shadow over his dream, and he says he "lies down in the shadow", accepting it in a way. No longer did his dreams light his way because he was dealing with the shadow. Only the shadow and the racism that was stopping him from achieving his dream guided him.
Part 3: But through hard work and persistence, he broke through the wall. He emphasizes that his "black" hands broke through that wall of racism to find his dream. He was able to break the shadow and become the person he wanted, a great poet, recognized for his work in the United States. He broke the shadow that had been obstacles to him and they turned into a thousand other hopes and dreams that brought light into his life.