The command man gives you access to an on-line manual containing a complete description of every command available on this system. It can provide you with one line descriptions of commands specified by name; or of all commands whose description contains any of a set of keywords.
To view the manual page for a command enter:
man name_of_command
For example,
man cp
will display the manual page for the cp command using the more pager by default.
The command
man -k keyword
displays a one line synopsis of each command that has "keyword" in its description. For example
man -k mail
displays a one line synopsis of each command that has the word "mail" in its description.
Enclose a phrase in single quotes to search for it.
man -k 'phrase to search for'
For example
man -k 'copy files'
You can print a manual page by piping the output of man through the lp command.
For example, the command
man cp | lp -d ps
will print the manual page of the cp command on the "ps" queue (A4 B&W).