As you can see, Norwegian cups are male, slices of bread are female and rolls are neutral. Sounds weird? Well, it is. But that’s just the way this language works. So, in Norwegian we have three translations for the English word a:
That means: you cannot say
et kopp - it’s just wrong. It has to be en kopp, because cups are male.
How can you possibly know that a cup is male and not female or neutral? Unfortunately - you can’t. You have to learn the gender of every single word by heart. Sorry! Perhaps you know this concept from another language, like German, French, Spanish, or Russian.
So if this has not been confusing enough, here is something else: Female Norwegian words (and only the female ones!) can also be male! So - you can say en brødskive instead of ei brødskive, but you cannot say
ei kopp instead of en kopp.
Why is that so? My advice is best not ask. But, if you really, really want to know, you will have to read about Norwegian language history.