New posts in Software Sources

Do files at /etc/apt/sources.list.d need to have an extension '.list'?

apt-get update only for a specific repository

What is the "proposed" repository?

How do I restore the sources.list file?

How to remove a repository?

How do I add a software source?

What is the difference between Debian contrib & non-free and how do they correspond to Ubuntu repositories?

How do I enable the "backports" repository?

How do I enable the "partner" repository?