Historically UNIX systems have kept the User's Manual, Programmers Manual and Administrator's Manual on-line collectively refered to as manual pages, or man pages. Linux follows this tradition. There is a move to replace the man pages with Texinfo (``info info'' will tell you more about Texinfo), and so many of the GNU man pages have a statement similar to the following.
This documentation is no longer being maintained and may be inaccurate or incomplete. The Texinfo documentation is now the authoritative source.
Man pages describe user commands, system calls, library functions, configuration file formats, devices, subroutines, and kernel internals, on the system. It is important for you to familiarize yourself with the use of man, since it is the most readily available source of information on how to use Linux. There is GUI interface under X called xman.
The man pages come in for a lot of criticism for being cryptic and taking for granted a lot of UNIX background. Each page contains information about a single command or file. The bottom of the page often contains references to other files and related commands. Sometimes these references help clarify, often not.
Man pages are divided into sections, according to what they are used for. User commands are in section 1, UNIX system calls are in section 2, subroutines 3, devices 4, and so on. Sometimes an entry in two sections can have the same name and sometimes you will see a number following the name of a man page. This number is a reference to the man page section the command is found. There are hard copy version available in bookstores. These are usually subdivided into sections correpsonding to the the same sections as the commands. For a complete description of the man command with all it's options, see the man subsection of the Commands section below.