"What's going on, Finlay?"
Translation:Dè tha dol, Fhionnlaigh?
It's vocative case. You lenite and slendarise (if possible) a name when addressing someone of that name.
Ciamar a tha Seumas? - how is James?
Ciamar a tha thu, a Sheumais? - how are you, James?
Have you read the notes? If you go on the desktop webpage for duolingo on your computer you will see the course notes.