Extensive online help is provided by the man(C) system. man is short for ``manual'', and is a tool for retrieving the text of the reference manuals.
In this book, you will sometimes see reference keywords followed
by a letter in brackets; for example,
The letter in brackets indicates the section of the reference manual
in which the keyword is discussed. If you are working at the shell
prompt, you can read the reference entry for the keyword by entering
the following command:
man [section] keyword
The section field is optional and is used to select a particular section when a keyword is documented in more than one section. For example, type man C kill to read the C section entry on the keyword kill (which is documented as a command in section C and a callable function in section S).
The reference manual entries are technical descriptions; they are not tutorials and make no concessions to the inexperienced user.