ls /usr/share/man/man?/* will show you all the man pages on your system. I used to pick ones at random.

Originally there were a number of manuals. Manual 1 had user commands. Manual 2 had system calls. Etc. You can type man NUMBER intro to read about that manual. You can also use man -k or appropos but I’ve also just used grep. These days they’re compressed so zgrep.