Cormac McCarthy begins No Country for Old Men in medias res, or "in the middle of the action," which is common for an episodic tale in which men are searching for each other (like The Odyssey, for example). McCarthy frames each chapter from Sheriff Bell's first-person dialogue in italics. Coming from an old man, Bell's words about the old lawmen of Texas yore stand in sharp contrast to the bare-bones action of the narrative. Bell's narration is parallel to the action: it doesn't match up or fill in any gaps. Instead, it serves as a mythology of its own, alluding to simpler times, before drugs and money caused border-crossing bloodshed.
The story-proper is told in the plain and simple style of third person. McCarthy's plot is search-and-destroy as he weaves together four men who are looking for each other: Chigurh, who is searching for Moss; Wells, who is searching for Chigurh; Bell, who is searching for Moss and Chigurh; and Moss, who is running from them all. McCarthy is able to omit unnecessary background information about these men because they are so motivated on finding each other and the money: all other details seem secondary in purpose.
Plotting a novel in which four men are after each other is very difficult to do and still make the plot linear or chronological, so McCarthy stages episodes instead, some of which run concurrently (at the same time). The places where Moss goes are random because he doesn't know where he's going (that's the point: the love of money causes one to lose direction).
Narrative gaps are part of the nature of fiction: an author's role in literature is to supply the question minus the answer. The answer, those gaps and the themes and symbols, are for us, the reader, to deduce. We may not know where Moss is going, but we must know where McCarthy is. And he uses Bell (who is very similar to him) as a guide.