Welcome on 
The main goal of this portal is to guide your first steps with Debian. It explains the basics of installation and how Debian works. This portal is designed for beginners. It uses a simplified informatic language. We recommend reading installation of Debian before starting here.
http://www.debian.org/doc/manuals/debian-reference/ch02.en.html – Debian official references
Apt - The main package management suite of tools
DebianUpgrade – How to upgrade your distribution
Backports – Your Debian stable runs great but the software is a little bit outdated compared to other distributions? This is where backports comes in.
See also: PackageManagement List of tools