As you may have deduced from the number, it's a prequel. It's even a proper prequel, best read after the works appearing before it only in the Real World timeline. Burlew alerts you to that in the Introduction. (As opposed to the Preface, provided by Redcloak because he has no role in it.)
As befits a world based on a role-playing game, some player characters have a lot of backstory; others have none. Belkar of course has none; explaining why he turned into the little sociopath would keep him from playing his comic relief role. Roy's father appears on stage to exemplify the back story that has caused so much problems. And Halley gets the letter that everyone knows from the webcomic.
Amusing little tales. Not much of an overall plot, obviously.