This reference guide provides very basic information on how to use and administer an Ubuntu Linux installation.
This book does not attempt to recreate the online manual, commonly known as the "man pages." Linux man pages are very consistent in format, complete, and useful.
When a very helpful soul in a forum politely requests that you RTFM, then consider using the following command:
man (command)
Brings up the manual page for the specified command.
But what if you don't know what command you are looking for?
apropos (phrase)
Lists commands that are "appropriate" for the phase provided.