Step 1: Visit the PPA’s overview page in Launchpad and look for the heading that reads Adding this PPA to your system. Make a note of the PPA’s location, which looks like:
Step 2: Open a terminal and enter:
sudo add-apt-repository ppa:user/ppa-name
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.