There is an immense amount of free stuff. The Linux Documentation Project has many mirrors (search for LDP).A local site: http://nix.itss.auckland.ac.nz/LDP/guides.html is a good place to start. Try looking at some online: click on gs/ for the Getting Started manual. The NAG2 : Network Administrator's guide tells you about network stuff. The System Administrator's Guide is good too.
At your bookshop or Public Library .. not in any particular order of merit:
Running Linux, by Matt Welsh et al. This is very good, (like all the books published by O'Reilly).
Mastering Unix, by KAte Wrightson et al. Sybex. A bigger book ...
Inside Linux, by Michael Tobler.
A practical guide to Linux, by Mark Sobell.
Linux - Installation, configuration and use, by Michael Kofler.
On, for example, a RH7.1 distribution CD: in a Documentation or doc directory: Getting Started guide, Installation Guide, Red Hat Reference Guide. In your installed system, in usr/doc, or usr/share/doc, or usr/Documentation ... all the HOWTOs.