The novel ties into the Dark Tower universe(s), and is broken down into three parts, or "books":
BOOK I: "Captain Trips"
In this first 400 pages or so (of the uncut 1142-page book), there is an outbreak of a manmade biological plague, which is spread to Texas, New York, Atlanta, New England and the southwest in a matter of days. We're introduced to the main characters, and their backstories, and we see the government panic as the superflu spreads as a plague, and we see the collapse of civlization as totalitarian martial law is enforced, thousands are killed to keep the government's lies under wraps, and what the characters on an individual level go through.
BOOK II: "On The Border"
In the wake of civilization's destruction via plague, the key individuals are trying to cope with the loss, until they are all united by dreams and visions of a 108-year-old black woman in Nebraska named Mother Abigail. Many of these protagonists find each other, and unite for a cross-country oddysey from various places headed for Nebraska. Meanwhile, however, other scattered survivors with darker natures are drawn via dreams and visions to a mysterious supernatural drifter in Las Vegas, who they refer to occuasionally as "The Dark Man" or "Walkin' Dude" and whose supposed real name is Randall Flagg. The other survivors find Mother Abigail and establish a new society in Colorado that they call the Free Zone. While the Free Zone is dedicated to a peaceful, democratic society in Colorado, Randall Flagg is setting up his society in Las Vegas, where he crucifies and tortures his disloyal, establishing a fascist rule. He influences people in the Free Zone to commit terrible acts of treachery, and it becomes clear that Randall Flagg's aggression can't "stand".
BOOK III: "The Stand"
In this last 400 pages or so, the story chronicles the heroes of the Free Zone going out from Colorado to Las Vegas for the final showdown against Randall Flagg.
The book was released in 1978, and then re-released uncut in 1990. In 1994, it as adapted into a TV miniseries starring Gary Sinise, Molly Ringwald, Rob Lowe, Ruby Dee and Jamey Sheridan. Not highly received amongst fans of the novel, but Sheridan playing Randall Flagg was actually praised well.
2: You have no sense of literature.