I'm still a bit confused. There seem to be so many different spellings of the same word and I can't tell which is the right - or preferred - one, when or why. Maybe it is just one of those things that either comes with time, practice and experience (+ patience!) or never comes at all.
Edited same day to include this:
According to Google translate, (Korean to English):
뭘, 뭐, 무엇이, 무엇, 무슨? = What, what, what, what, what?
The other way around, (English to Korean), is worse:
What = 무엇, 어떤 일, 어떤 것, 얼마, 웬, 얼마나 많은 금액, 얼마나 많은 양, 무슨, 얼마나, 어느 정도 and 본질.