Moi Naelle (Hey Naelle) Who are you? - Kuka sinä olet? To break it down, kuka means who. Sinä means you. olet means "you are" Out of politeness you would say "Kuka sinä olet?" however kuka olet would be understood. What's your name? - Mikä sinun nimesi on? Mikä - what sinun - your nimi - name (because you are asking what somebody else's name is, you add the suffix "si" so it becomes nimesi. on - is I am not a native speaker however I tried to help to the best of my ability. I hope it helped a little :) Onnea! (Good luck!)

WalkingAlone already gave a good answer. A few things though - "sinä" is not used to mark politeness, it simply means "you(sg)". The given phrases are correct and formal. Conversationally, you can also say: Kuka sä oot? (Who are you?) and Mikä sun nimi on? (What's your name?) -Jukka