How are you?

How are you? It's very common sentence in English language. But it's actually informal sentence. Different times use you different format of 'How are you?'

1. How are you doing?
2. How do you do?
3. How have you been?
4. What's up? 
5. How is going?

Answer this question 

1. Fine.
2. Very well.
3. Fine and you?
4.  I am doing well. 
5. Fine, thanks.
6. I am doing very well.