The Debian web site contains a large quantity of documentation about Debian. In particular, see the Debian GNU/Linux FAQ and the Debian Reference. An index of more Debian documentation is available from the Debian Documentation Project. The Debian community is self-supporting; to subscribe to one or more of the Debian mailing lists, see the Mail List Subscription page. Last, but not least, the Debian Mailing List Archives contain a wealth of information on Debian.

If you need information about a particular program, you should first try man program, or info program.

There is lots of useful documentation in /usr/share/doc as well. In particular, /usr/share/doc/HOWTO and /usr/share/doc/FAQ contain lots of interesting information. To submit bugs, look at /usr/share/doc/debian/bug*. To read about Debian-specific issues for particular programs, look at /usr/share/doc/(package name)/README.Debian.

A general source of information on GNU/Linux is the Linux Documentation Project. There you will find the HOWTOs and pointers to other very valuable information on parts of a GNU/Linux system.

Linux is an implementation of Unix. The Linux Documentation Project (LDP) collects a number of HOWTOs and online books relating to Linux.

If you are new to Unix, you probably should go out and buy some books and do some reading. This list of Unix FAQs contains a number of UseNet documents which provide a nice historical reference.