MAN PAGES
While they're not all well-advertised, there are actually a variety of means of getting help under Unix. The most important and reliable of these are `man' pages. Man pages correspond to online manuals for programs, file formats, functions, system calls, and so forth. You might have asked a UNIX question on a newsgroup only to get back as a reply RTFMP ( Read The "Fantastic" Man Pages ). If you've never read one before, the best way to start is by typing 'man man' at the command line.
Of course, while man pages are a vast improvement over the online documentation of most other OSes, they suffer from many failings:
some people don't like to read text on the screen
not very helpful unless you already know what to look for
not always accessible even when present
not always present, especially under Linux