"They are drinking coffee."

Translation: One piją kawę.

[YariMsika]

Why would it not be kawa?

[Macixx12]

Because of declension, kawę is biernik
There is rule, which helps to know which one case is, for example biernik answers the questions: who? what? (I see) kto? Co? Widzę
Co widzę? - Kawę, what i see? - coffee
in english it doesn't make any sense but in poland this is the way to learn it. Declension is the reason why this language is hard and even we have sometimes problem with that, good luck

[Cosmopoiesis]

If "kaw" us not a word then what sounds do Polish crows make?

[Jellei]

I think it's "KRA!"

[OleTok]

Dlaczego "one", a nie "oni"?

[Macixx12]

in this context it does not matter as there is no indicated person / gender