The sources.list is a text file on a Debian derived Linux distributions. Aptitude (apt-get) uses this list of servers as locations from which to retrieve software. To add to this you must be logged into a terminal. Have ready and know how to use a simple terminal text editor such as nano or vi. Open the sources.list file in your text editor. I prefer nano text editor so the command will look like:
sudo nano /etc/apt/sources.list
You must sudo this command unless you’re already switched to the super user account via: ‘sudo -s’. Now add or delete any lines you need to, then save. The next apt-get command you run will now pull from these servers.