PPA's (Personal Package Archives) contain software that is not offered by default in Ubuntu. PPA's include various software including themes, utilities and standard programs.
1 Software & Updates
Open the Gnome Launcher and click on Software & Updates. Click on the second tab called Other Software.
2 Add a PPA
Click on Add. Enter the PPA name, these follow the format of ppa:starlabs/ppa
3 Remove a PPA
To remove a PPA, select the PPA and click remove.
Please note: This will only remove the PPA itself, any software installed via this PPA will not be removed.