Greetings. How do I install the following: sudo add-apt-repository ppa:starlabs/ppa
The folowing Would have helped
https://launchpad.net/~starlabs
For ppa's the first question is, do I really need this?
For Debian, it has been painfully evident that the addition of Ubuntu based ppa can cause problems. It can make your system actually go #! (Crunch Bang). Myself, I do have virtutalbox, and SpiderOak (cloud backup) ppa's that are for both Debian and Ubuntu - but I have researched and they are large companies that wish to be mission critical software for any os or distribution they support.
Whenever you see "Launchpad" it is a hint that the ppa is quite Ubuntucentric and has a higher risk of making problems for you.
Short answer - it goes into /etc/apt/sources.list.d/ I would use nano in a terminal, but there are (as usual in linux) various other ways to do it and some might be more effective.
man apt discusses the edit-sources option which is described as a work in progress.