Words for asking

どうした？ (doushita?) = What Happened?
なに？ (nani?) = What? 
質問 (shitsumon) = Question.
だれ? (dare) = Who?
いつ? (itsu) = When?

どうして？ (doushite?) = Why?
なぜ? (naze?) = Why?
なんで? (nande?) = Why?

If you want to ask why, you can use naze or doushite or nande.
If you want to ask how, you can use doushite or nande, but cannot use naze. 
Doushite and nande are used not only to ask why but to ask how.