Basic Vocabulary - easy and must 💯

hi (to younger person, between friends) 
hi (in social relationships, between colleagues, or strangers on the street, for example) 
hi (in the formal setting - presentation, announcement)

안녕?
안녕하세요? 
안녕하십니까?

how have you been? (between friends - in terms of being the same age, mostly) 
how have you been? (in informal polite form - most social relationship)

how are you? how have you been? 
It is basically the same as '잘 지냈어요?' but just expressed differently.

어떻게 지내? 
어떻게 지내요? 
어떻게 지냈어요?

what's up? 
what are you up to? 
Something good? Anything new?

a Casual form of bye! or Go well! 
Go well , informal polite form (when you are staying and the other person goes away/ leaves) 
Stay well (when you are the one leaving, and the other person stays)

잘 가 
안녕히 가세요 
안녕히 계세요