Why = 왜 (you can add 요 to it if its used alone; 왜요 makes 왜 formal)

왜 왔어요?

Why did you came?

왜 했어요?

Why did you do it/that?

왜 안 먹어요?

Why don't you eat? (As in why are you not eating? Is something wrong?)

왜 서울 가고 싶어요?

Why do you want to go to Seoul?

왜 웃어요?

Why laugh?

왜 연락 안 했어요?

Why didn't you contact me? (연락 = contact)

왜 전화 안 했어요? (전화 = phone call)

Why didn't you call me?

왜 혼자예요?

Why are you alone?

왜 가요?

Why do you go?

왜 말 안 했어요?

Why didn't you tell me? (Literally why didn't you talked)

왜 말 하지 않아요?

Why don't you tell me? (Literally why don't you talk)

That's it~

안녕♡