Well, son, I'll tell you:
Life for me ain't been no crystal stair.
It's had tacks in it,
And splinters,
And boards torn up,

 The first line of the poem orients us to the speaker of the poem: a mother, talking to her son. 
 The poem begins with the mother speaking in  metaphor , comparing her life to a staircase. The  imagery  of a “crystal stair” can be associated with a perfect life where everything goes right. She tells her son, in colloquial, familiar language, that life hasn’t been the best to her.
Mother to Son