Mother To Son is typical of what you would expect from such a title - a mother wanting to give her son the best advice based on her own experiences. The mother relates these experiences by comparing life to a staircase
meant to symbolize the journey of life.
It is an apt metaphor as a staircase has "ups and downs" and, when life is hard, there is no need to give up; just as the mother herself has been "... reachin' landin's,/ And turnin' corners..."
Any particular experience- or life itself - may appear to be a "crystal stair" with all you could imagine from a glittering and glamorous life. She reminds her son that her "crystal stair" has had it's fair share of "...tacks in it, / And splinters."
The mother wants her son to understand that he can withstand all the hardships and that it will be worth it but that he must not "turn back" or "sit down." The message is clear. The son must persevere.