If you like you can use the one I use, or if you want the US one its
If you want sarge instead just change "sid" to "sarge"
Sid is the unstable branch, Sarge is the testing branch, that means sarge will eventually become the next Debian release, sid will always have the latest packages.
"apt-get update" retrieves the package list from the sources specified in your sources.list so you need to do it first.
apt-get makes it easier to update your system and install software packages. For example when Debian Sarge comes out, all you need is have your apt source(s) point to the sarge(or stable which it will become) then do "apt-get dist-upgrade" then it'll automatically download and install all necessary packages for upgrading to Sarge.
Check out the Debian documentation if you want to know more: