When meeting people, we usually say an expression like Good morning/Good afternoon/Good evening. This is relatively formal. In a very informal style, we can say Hello or Hi.
When we meet people, we often greet them by shaking hands and saying ‘How do you do?’ or ‘Nice to meet you.’

Good morning Maria. How are you?

Hello Jane. How are things with you?

Note that we do not usually shake hands with our close friends or family members. We greet them by just saying ‘hello’ or ‘hi’.

When we meet people we know, we politely ask about their health or general well being.

Common expressions are:

How’re you doing?

How’re you?

How’s it going?

How’s things? (very informal)

How’re things?

Formal answers are:

Fine, thank you.

Very well, thank you. And you?

Informal answers are:

OK.

Fine, thanks.

I’m good, thank you.

Great, thanks.

I’m alright.

Not too bad.