How to Configure sources.list on Linux Debian 9

This is a brief guide on how to configure sources.list file on Debian 9, codenamed stretch. Debian is one of the, most popular Linux distributions and much of its strength comes from the core of Debian package management – apt. Everything in Debian, be it an application or any other component – is built into a package, and then that package is installed onto your system (either by the Installer or by you).