What do the numbers in a man page mean?
The number corresponds to what section of the manual that page is from; 1 is user commands, while 8 is sysadmin stuff. The man page for man itself (man man) explains it and lists the standard ones:
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 Deamons Distributions customize the manual section to their specifics, which often include additional sections.
There are certain terms that have different pages in different sections (e.g. printf as a command appears in section 1, as a stdlib function appears in section 3); in cases like that you can pass the section number to man before the page name to choose which one you want, or use man -a to show every matching page in a row:
$ man 1 printf $ man 3 printf $ man -a printf
You can tell what sections a term falls in with man -k (equivalent to the apropos command). It will do substring matches too (e.g. it will show sprintf if you run man -k printf), so you need to use ^term to limit it:
$ man -k '^printf' printf (1) - format and print data printf (1p) - write formatted output printf (3) - formatted output conversion printf (3p) - print formatted output printf [builtins] (1) - bash built-in commands, see bash(1)