ABOUT:
なぜ and どうして both mean "why" and are basically interchangeable. A third "why" is なんで which is used the same way as the other two but is more casual.
Examples:
なぜ日本語を勉強していますか?
Why are you learning Japanese?
[why | Japanese | studying?]
どうして、そんなに歴史に詳しいですか?
How come you know so much history?
[why | such an extent | history | detailed/well-acquainted with]