PPAs (Personal Package Archive) provide additional resources. They are small repositories you can add to get some special content.
You can add them with Bash:
sudo add-apt-repository ppa:<repository-name>
Lets make an example:
If you want to install Clipgrab, you add the repository first:
sudo add-apt-repository ppa:clipgrab
Then you have to update your sources:
sudo apt-get update
Now you can install clipgrab the usual way:
sudo apt-get install clipgrab
Further Reading
- Repositories and the CommandLine
- Clipgrab (German)