Hey, Deanoe.
So, you'll need to download the 'cores' in retroarch that correspond to what the .INI is looking for. Hyperspin uses .INI files to do... everything pretty much. Cores are basically emulators.
Then, you'll need a system .INI file for the 2600. I recommend you copy a working system, name it Atari 2600 and go from there.
Those .INI files are in the settings folder. This will serve as a good road map as to what's going on.
That should get you started, hope that helps!
-ghost