In the poem it talks about a mother explaining to her son that her life wasn't clear for her but he still can go through a great life in a clear way.
She said " Life for me ain't been no crystal stair. It's had tacks, and splinters, and boards torn up, and places with no carpet on the floor". She's trying to say she's been through up's and down.
At the end of the of the poem she tell's him " But all the time Iv'e been climbing on, and reachin’ landin’s, and turnin’ corners".And sometimes goin’ in the dark Where there ain’t been no light. So boy, don’t you turn back. Don’t you set down on the steps ’Cause you finds it’s kinder hard". She's guiding her son through a great path, and wants him to have a great clear stair that she didn't have. Also want him to keep climbing up that clear stair he stills need to walk on and go on.