"It was a fascinating lesson in time history--a truth-is-stranger-than-fiction marvel, to say the least. I feel like a Tinkertoy kid building my own self out of one of those toy building sets; for as she laid her life before me, I reassembled the tableau of her words similar to a picture puzzle, and as I did, so my own life was rebuilt."
An interesting thing happens to James McBride, the author of The Color of Water. He always felt as if there was something, some key to his past, which would help him understand his place in the world. It is true that he got many mixed messages from his mother, Ruth, who assiduously avoided revealing anything about her past, and these contradictions were significant enough for McBride to wonder, clear into his adult life, what created them.
To unravel his own family heritage, McBride has to get his mother to talk about her past. She gives him the barest of clues, not knowing (or even much caring) if it would lead him anywhere. It does, and this book recounts both of their stories in alternating chapters.
The quote you mention, which compares his task of piecing together his mother's (and thereby his own) past to building something out of Tinkertoys, is what McBride spends much of the book doing. He wants to know why his mother is obviously white but acts and lives as if she were a black woman. He needs to understand his mother's complicated views on religion and why she refuses to let her children talk about their family to others. More than anything, he needs to know why she refuses to talk meaningfully about any of these things.
For many years, his own life is complicated and even shaped by these contradictions and his mother's silence; and he believes that he can only know his present if he discovers his past. Your question asks how McBride portrays this theme; he does it through simple storytelling. He juxtaposes his story with his mother's story.
As he completes his journey and his storytelling, however, McBride discovers that he was wrong. He says:
Sometimes without conscious realization, our thoughts, our faith, out interests are entered into the past. We talk about other times, other places, other persons, and lose our living hold on the present. Sometimes we think if we could just go back in time we would be happy. But anyone who attempts to reenter the past is sure to be disappointed. Anyone who has ever revisited the place of his birth after years of absence is shocked by the differences between the way the place actually is, and the way he has remembered it. He may walk along old familiar streets and roads, but he is a stranger in a strange land. He has thought of this place as home, but he finds he is no longer here even in spirit. He has gone onto a new and different life, and in thinking longingly of the past, he has been giving thought and interest to something that no longer really exists.
He has, as the quote says, "rebuilt his life" with the facts he learns about his mother's past. His quest to discover his mother's heritage is successful; his greater discovery, however, is that his past no longer defines his present or his future.