During my learning I have noticed one sentence:
Bis Ende des Monats
I have found an information that we create genitive case for maskulinum and neutrum by using des and adding s to a noun. So, in my opinion, the sentence above matches this description. But my problem is that I do not see any genitive case here.
From what I know, genitive case answers the question wessen?. While, in my opinion, in the sentence above we have nominative case: wer? was? -> Monat.
So why is genitive case used here? Am I wrong in my way of thinking?