If you are new to Unix, you probably should go out and buy some books and do some reading. A lot of valuable information can also be found in the Debian Reference. This list of Unix FAQs contains a number of UseNet documents which provide a nice historical reference.

Linux is an implementation of Unix. The Linux Documentation Project (LDP) collects a number of HOWTOs and online books relating to Linux. Most of these documents can be installed locally; just install the doc-linux-html package (HTML versions) or the doc-linux-text package (ASCII versions), then look in /usr/share/doc/HOWTO. International versions of the LDP HOWTOs are also available as Ubuntu packages.