When we see someone we know, we usually exchange greetings:
Hello, how are you?A:
Fine, thanks. How about you?
When we leave people, we usually say something as we leave:
See you later.B:
We use Good night only when we are leaving someone at the end of the day, before going home or going to bed:
[leaving someone’s house]
Good night. Thanks for a lovely evening.
[before going to bed]
I’m off to bed. Good night.
Congratulating and celebrating
We use different expressions for celebrations:
on special occasions
to wish someone luck before an important event
to congratulate someone
We don’t say congratulations to wish someone a happy birthday:
Happy birthday, Nora.