does this mean glasses like cups or glasses like eye glasses?
The former.
So we use ny for singular and nye for plural?
yes
What is glasses (the kind that you wear over the eyes) in Norwegian?
it's briller
When do you use nye and nytt?
Nye is used for plural nouns and nytt is used for singular neuter nouns. :0)
Why isn't it "De glassene er nye" ?