I’m always forgetting what they mean and how to use them.
There’s a great answer at: https://unix.stackexchange.com/a/3587/223606
For me, the important parts are:
MANUAL SECTIONS The standard sections of the manual include: 1 User Commands 2 System Calls 3 C Library Functions 4 Devices and Special Files 5 File Formats and Conventions 6 Games et. al. 7 Miscellanea 8 System Administration tools and Daemons Distributions customize the manual section to their specifics, which often include additional sections.
And the syntax:
$ man 1 printf $ man 3 printf $ man -a printf