Manpage names are not tied to command names at all. Sure, sections 1 and 8 are conventionally sorted by command name, but the other sections have different purposes. Sections 2 and 3 document system calls and library calls, one function at a time:

  man 2 fork
  man 3 fread

Section 5 documents file formats and conventions:

  man 5 passwd
  man 5 rsyncd.conf

And section 7 is described by `man man` as "miscellaneous". There is some nice high-level overview documentation hidden in there, e.g.:

  man 7 signal
  man 7 socket

My all-time favorite is from section 7 is `man ascii`. Very handy when you're ever pushing bits.

NOTE: If these commands fail for you, check if you have the "man-pages" package installed (may be called different in your distro).