Can "studera" be used like English "study" to mean that you make an effort to go over your notes after class (German "lernen"), or does it only mean study at university (German "studieren")?
It means both, but it's rarely used in daily conversation, especially among young people. The more colloquial word "plugga" is used much more often, especially when talking about studying for an exam.
Is 'plugga' the equivalent of 'cram' when one is cramming for an exam, meaning studying really hard?
I just finished my lesson of Adjectives and Adverbs in my book, and I find this helpful lesson
Sure, added it. Do note that it's less idiomatic unless in context, though.
I'm pretty sure this is the first time I've seen the word varje. I've been systematically logging all new vocabulary (helps me learn it) in an excel file and it's not there.
Quite possible - it's taught in the second lesson of this skill ("Determiners"), and Duolingo will occasionally forget to teach you new words you are supposed to be shown. It's rare, but certainly not unheard of. I also log all new words I come across in other courses meticulously, and it's happened to me a few times as well.