It's not a package, it's a repository; a collection of dozens of packages that are designed to work with the apt package manger. And it's designed for use with Debian, not Ubuntu.
Now since Ubuntu is based on Debian, it's likely that most of the packages available there will work, but if you do decide to use it, don't go blaming anyone else if something you install destroys your system.
How to use it is explained right there on the page. Find the setting that most closely matches the architecture, distribution and version you're running, and add that line to your /etc/apt/sources.list file (or through the corresponding "add source" function in the gui program manager). Then just reload the list and the new packages should be available for installation.
You'd probably be better off finding a source that's made especially for your distribution though.
Last edited by David the H.; 02-18-2010 at 12:13 PM.