Add additional software repositories
Software is available from third-party sources, as well as from the default Ubuntu software repositories. If you want to install software from a third-party software repository, you must add it to Ubuntu's list of available repositories.
Only add software repositories from sources that you trust!
Third-party software repositories are not checked for security or reliability by Ubuntu members, and may contain software which is harmful to your computer.
Install other repositories
Click on the Ubuntu Software Center icon in the Launcher, or search for Ubuntu Software Center in the search bar of the Dash.
When the Software Center launches, click Edit ▸ Software Sources
You will be asked to enter your password. Once you have done that, switch to the Other Software tab.
Click Add and enter the APT line for the repository. This should be available from the website of the repository, and should look similar to:
deb http://archive.ubuntu.com/ubuntu/ precise main
Click Add Source then close the Software Sources window. Ubuntu Software Center will then check your software sources for new updates.
Activate the Canonical Partner repository
The Canonical Partner repository offers some proprietary applications that don't cost any money to use but are closed source. They include software like Skype, Adobe Reader and Adobe Flash Plugin. Software in this repository will appear in Ubuntu Software Center search results but won't be installable until this repository is enabled.
To enable the repository, follow the steps above to open the Other Software tab in Software Sources. If you see the Canonical Partners repository in the list, make sure it is checked then close the Software Sources window. If you don't see it, click Add and enter:
deb http://archive.canonical.com/ubuntu precise partner
Click Add Source then close the Software Sources window. Wait a moment for Ubuntu Software Center to download the repository information.