"Ми у квартирі."

Translation: We are in an apartment.

[human5421993989]

Could someone please explain to me the use of the preposition "у" compared to "в" and "на"?
Couldn't we say "ми в квартирі"?

[Tielbert]

У and в are pretty same, they are interchangeable in order to avoid many consonants or many vowels on a row. В квартирі would contain too many consonants in the beginning.

На is a completely different preposition, it means ON.