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".
Daughter is tytär in Finnish.
Boring is tylsä in Finnish.
Yes is "kyllä" in Finnish.
Black is musta in Finnish.
In the beginning is alussa in Finnish.
Pie is piirakka in Finnish.
Wonderful is ihana in Finnish.
Friendship in Finnish is "ystävyys".