I found really useful documentation for Linux beginners.
"This Debian Reference (http://qref.sourceforge.net/) is intended to provide a broad overview of the Debian system as a post-installation user’s guide. It covers many aspects of system administration through shell-command examples. Basic tutorials, tips, and other information are provided for topics including fundamental concepts of the Debian system, system installation hints, Debian package management, the Linux kernel under Debian, system tuning, building a gateway, text editors, CVS, programming, and GnuPG for non-developers."
This book is devoted to Debian system but it is topical for some other Linux systems.