A handful of phrases will carry you through your first day in Helsinki:

Finnish	English	When
Hei!	Hi! / Hello!	Any time, with anyone — the safest greeting there is
Moi!	Hi!	Casual and very common, especially in Helsinki
Huomenta!	Morning!	Until about mid-morning
Mitä kuuluu?	How are you?	Literally “what is heard?” — with people you know or have just met

The usual answer is Kiitos, hyvää. — Fine, thanks. Then pass the question back: Entä sinulle? — And you?

To give your name, say Minä olen Marina. — I'm Marina. Or simply Olen Marina. Meeting someone for the first time, add Hauska tavata! — Nice to meet you!