Mitä sinä teet? (Sounds a bit like you're suspicious of what someone is doing)
More natural: Mitä teet? or Mitä puuhaat.
But you should try to find a proper way to pronounce it. Otherwise it's going to sound odd.
For you is sinulle in Finnish.
How is miten in Finnish.
I am not Finnish. - (Minä) en ole suomalainen.
Finnish legend in Finnish is "suomalainen legenda".
Yes is "kyllä" in Finnish.
Boring is tylsä in Finnish.
Daughter is tytär in Finnish.
Black is musta in Finnish.
Food is ruoka in Finnish.
Library is kirjasto in Finnish.
Queen is kuningatar in Finnish.
In the beginning is alussa in Finnish.