man -aw [subject] - shows the files corresponding to all entries for a subject.
man -k = apropos - searchs name and detail description
man -f = whatis - searches one line summaries

Man sections
1   Executable programs or shell commands
2   System calls (functions provided by the kernel)
3   Library calls (functions within program libraries)
4   Special files (usually found in /dev)
5   File formats and conventions eg /etc/passwd
6   Games
7   Miscellaneous (including macro  packages  and  conventions), e.g. man(7), groff(7)
8   System administration commands (usually only for root)

Man searches the $MANPATH for its entries. Usually these entries are stored in gz format in /usr/man/ (or /usr/share/man/). Uses the $PAGER variable to present the output.

/etc/issue - shows text on console when you log in locally
/etc/issue.net - shows text on console when you log in remotely
/etc/motd - moto of the day - displays on all logins

You can search for help online (stupid):

- The linux documentation project
- Online guides
- Vendor sites
- Mailing lists