I recently posted an answer where I wrote add the PPA. But I now realize, that I have no idea what the difference between a PPA and a Repository is. So can someone please explain it to me?
On systems like Ubuntu, most software is packaged in nice .deb (or .rpm, like in Red Hat) files which contain the programs and libraries you need. These files can be downloaded or come in CDs (Ubuntu's CD is full of them). Repositories are servers which contain sets of packages.
Personal Package Archives (PPA) allow you to upload Ubuntu source packages to be built and published as an apt repository by Launchpad.
Also see What are PPAs and how do I use them?
and Wikipedia.
To sum it up:
