Back in the early days, the printed manuals for Research Unix and BSD consisted of two volumes. Volume 1 was the reference and consisted of all the man pages for every command (section 1), system call (section 2), library function (section 3), etc. Volume 2 contained longer documents - what this article calls tutorials, how-tos, and explanations.

The man command let you read all the pages in volume 1. Volume 2 only existed in print, with the troff source in /usr/doc but no obvious way to find it if you didn't know where to look. So naturally volume 2 fell by the wayside. When I was learning Unix in the late '90s and early '00s I had no idea there was supposed to be "official" documentation besides man pages, and filled in the gaps with random web tutorials and borrowed O'Reilly books and other "unofficial" sources.

Nowadays some "Unix purists" are insisting that man pages are all the documentation you could ever possibly need, and if the man page is too long that means the software is too bloated. I find that attitude to be ahistorical. Like anyone's going to learn to effectively use troff and eqn from a cut-and-dried syntax description.

(I could ramble a bit about the other documentation formats that have sprung up to replace troff and how, nice as they can be, they don't replace the convenience of manpages, but this comment is long enough.)