In The Life and Opinions of Tristram Shandy, Gent, Laurence Sterne is neither unable to present a straightforward story or deliberately trying to frustrate readers. Rather, he is quite literally presenting both the life and the opinions of the narrator, Tristram Shandy, in order to comment on his own society through his book. Let's look at this in more detail.
Through nine "books," the title character and narrator speaks of his own life and the life of his family. He also inserts plenty of his own opinions and intersperses plenty of stories and sermons, rants and essays, and even legal documents. There is a narrative in this book. In fact, there are actually two narratives: one surrounding Tristram and the other surrounding his uncle, but they are not especially chronological.
What Sterne is really doing is comically critiquing everything from family life to literature to health to pseudo-science. One of Sterne's major focal points is the writing process itself. Tristram is a writer who is trying to tell a story, but he is not doing it overly well, since he keeps making long digressions. Other writers of Sterne's time did this as well, and Stern is poking a bit of fun at them through his own character.