Problems since my new O.S. Linux 16.04

[sylas]

HI all ! At my last O.S. : 1. sudo apt-get build-dep $package 2. apt-get source $package
and I had all files.
Now with my O.S. Linux 16.04 it doesn't work.
At the end of 1. terminal says: Reading package lists.... Done E: You must put some 'source' URIs in your sources.list (I don't understand that ! )
At the end of 2. terminal says exactly same things as for 1. (above).
I hope somebody will help me.

[wOOnder]

Hello

We are on a french board so why asking us in english ?

Regards