What is the standard source list file for 18.10?

Okay I’ve badly damaged my package system. So I found another solution, sudo apt-get build-dep

I typed sudo apt-get build-dep update-manager Reading package lists… Done E: You must put some ‘source’ URIs in your sources.list

Then I accessed it using the sudo nano /etc/apt/sources.list. The list was blank. Now I’m unsure on how to add more source URIs. I cannot access the software updates to change it.