The help chapter provides information on how you may access the documentation of the GNU/Linux system. There is normally a document describing every single tool you have installed, even if its only brief...
Also try: Specifying the section of the manual page, sometimes the man page is different for the same tool in different sections, note sections are numbered 1 to 9. Use apropos to find which section number to look in.
The syntax to look at a different section is:man section_number tool_nameFor example:man 2 timeThis will show you the man page called time in section 2, the equivalent page in section 1 is completely different
Search the manual pages for a string, as in it will search all manual pages for a particular string within each individual man page, it will then prompt whether you would like to view each page it will find. Use double quotes “ and ” if there are spaces in the string you are typing.
Please be warned that this method is going to be really, really slow. You are searching *all* man pages for a string
Equivalent to whatis: This command is the same as running whatis
Root Privileges: This takes some time and you require root privileges to do this.
Equivalent to...: apropos is the same as doing man -k (lowercase k).
Please note: You need to run makewhatis (as root) so whatis, man -f and apropos will work.