0 used to ask for specific information -- quel [ masculine, singular ]
1 emphasizes a description -- quel [ masculine, singular ]
2 used to ask for specific information -- qu’est ce qui
3 the thing that is being talked about -- ce qui
She told me what had happened. Elle m’a dit ce qui est arrivé.
4 used to ask about the purpose of sth -- pourquoi
What did you do that for? Pourquoi avez-vous fait ça ?
What’s this money for? A quoi est destiné cet argent ?
5 used to ask why -- pourquoi ?
“I told them to leave.” “What for?” “Je leur ai dit de partir.” “Pourquoi ?”