In one sentence-as if it were a thesis statement-summarize Liars' Club as if you explained it to someone who didn't understand it.

The Liars' Club is a memoir by Mary Karr in which the reader is expected to discern between the facts and the fictions Karr tells, just as Karr must learn to distinguish between fact and fiction in her own life to arrive at the core of love that persists between she and her mother despite all of her family's dysfunction.
As he explains in his introduction, Karr's book influenced Stephen King to pen his book, On Writing. In the first part of that book (the second deals with the mechanics of writing), King tells the story of his own dysfunctional upbringing and the genesis of a horror writer.
Karr's memoir describes a rough childhood marred by divorce amid the pollution of Texas oil refineries, time in Colorado, and Karr's grit in surviving it all.