Hello! 
I wonder what the difference is between カップ and コップ. Is there a difference or can they be used interchangeably?
According to this website and a quick google:
コップ is used for any cup or mug, and is a general word for either.
カップ is specifically a cup/mug with a handle that you’d drink hot drinks out of.
グラス is a glass (cup).
Thank you!
In my Japanese class last week we learned マグカップ which I guess is another way of saying カップ, leaning into the mugness of a cup?
So, for this sort of “what’s the difference between these two nouns” question, Google Image Search can help quite a lot. Stick each of them into the search box one by one, and see what sort of images it gives you.
Don’t forget the difference between グラス and ガラス which both mean glass but of course different, distinguishable kinds 
And also the difference between ガラス and カラス 
And カラス and クラス?
Any word, really.
ガラスグラスカップコップ is a cohesive construction