debian sources.list

An entry in /etc/apt/source.list consitsts of 3 parts, which are 1) URL, 2) distribution, and 3) area.

• URL is where you can download the software packages. For example,
  
• Distribution is the current version you would like to install. There are three main distributions: stable, testing, and unstable. User can also specify the code of the debian release, i.e. squeeze for debian 6.0.0.
  
• Area are assorted according to the policy of debian authority. Main is for softwares that completely comply with the DFSG (Debian Free Software Guidelines). Contrib is for the softwares that rely on the softwares can not complete obedient to DFSG, that is, non-free packages. Besides main and contrib, non-free packages suffers some issues of patents.

Here are examples of entries of /etc/apt/sources.list

deb http://ftp.tw.debian.org/debian/ squeeze main contrib non-free
deb-src http://ftp.tw.debian.org/debian/ squeeze main contrib non-free