I'm a computer science major at a summer internship. I've taken most classes in my major except Operating Systems & Distributed Systems.
What do I need to understand in order to set up a lightweight demo of GCM / FCM for phone.
I've programmed in Android Studio before, but it was mostly interface design.
the best place to start is probably with a complete working example. That you can find right here on Firebase Cloud Messaging Quickstart. This starter guide should answer questions such as "what you need to understand to setup FCM".
Please follow the above Firebase Cloud Messaging guide and try to get your FCM going. You can always post here when you encounter problems after you have failed to resolved them on your own.