Welcome to the first special weekend edition of Tool of the day (totd).

This special is about the most needed tools for any unix user, novice or expert alike.

At the end of my first totd I pointed you to the man or manual page for ls.
The 'on-line reference manuals' or man pages as they are commonly refered to are available for most, if not all, common *nix tools.

The most common way to use these is to just type man command.
A better way is to use man section command in this way you are sure to get the correct page.
Sections:
1   Executable programs or shell commands
2   System calls (functions provided by the kernel)
3   Library calls (functions within program libraries)
4   Special files (usually found in /dev)
5   File formats and conventions eg /etc/passwd
6   Games
7   Miscellaneous  (including  macro  packages and conventions), e.g. man(7), groff(7)
8   System administration commands (usually only for root)
9   Kernel routines [Non standard]

There are a lot of options to man, see: man man but you'll proppably never need to use them..
One of the options you might need to use is the -a or --all option will show all pages matching your query, not just the first.

There are also some derivate programs of man..

The -f or --whatis option spawned the whatis tool, it just displays the titles of the manual pages for your query, that might save a lot of time reading the wrong manual page.
~$ whatis man
man                  (1)  - format and display the on-line manual pages
man                  (7)  - macros to format man pages
man.conf [man]       (5)  - configuration data for man

apropos is another option turned application is the -k or --apropos option, this can be used to search for a word in the titles as shown by whatis.
~$ apropos bash
bash (1)             - GNU Bourne-Again SHell
rbash (1)            - restricted bash, see bash(1)
bashbuiltins (1)     - bash built-in commands, see bash(1)
bashbug (1)          - report a bug in bash


These tool should help you out of any problems you might encounter while useing a unix or unix like operating system.
Another usefull place for information on your system is the info tool..

You can start at the index by just calling info without any arguements..
You can also start info at a node or subnode of your choice, for example info bash variable will give a list of usefull Bourne-Again shell variables.

The info utility also has an apropos like feature.. This is done with the --apropos=keyword option..
~$ info --apropos=apropos
"(gdb)Help" -- apropos
"(info)Info Search" -- info-apropos
"(info-stnd)Invoking Info" -- Apropos, in Info files
"(info-stnd)Searching Commands" -- index-apropos


This information was based on man (man pager) 1.6b, man-db (db man pager) 2.4.3 and info (GNU texinfo) 4.8