I am not a native English speaker, what does it mean to feel at home? Does it mean feeling like one was at home, or something different?
It usually means that you are someplace that is not your home, but it feels like home (you are at ease, feel welcome and included, cozy and heartwarming).
Thank you. Enjoy those 3 lingots :-)
When does one use hjem and hjemme? (what is the difference)
Depends if it is a noun (et hjem, hjemmet, hjem, hjemmene/hjemma) or an adverb or preposition (hjem, hjemme).
Du er hjemme i hjemmet ditt. You are at home in your home
Why the 'seg'?
It is because you "feel yourself" as something (hjemme, ensome, glad, ...) in Norwegian. (I assume, because it's the same in German)