John, how are you? Professor Sana

We use first names only in informal situations:

A:

I saw Mel earlier today.

B:

Did you? I haven’t seen her for weeks.

We use first name + family name (surname) when we are not sure if the person we are talking to knows who we’re talking about:
Do you know Simon Perry?

Joy Goodfellow had to go to hospital today. I’m not sure why.

We use a title (Mr, Mrs, Ms, Dr, Prof) and the surname in more formal situations. We don’t usually use the title alone, or the title and first name (although we sometimes use a job title):

Dr O’Donnell, can I ask you a question?

Not: Dr David, can I ask …?

Could you ask Mrs Zatta to call me when she gets back?

Not: Could you ask Mrs to call me …?

We use Mr /ˈmɪstə(r)/ for men. We do not usually write ‘Mister’ in full. We use Mrs /ˈmɪsɪz/ for married women.

Ms /məz/ does not indicate if the person is married or not. Some women take on their husband’s surname and the title Mrs when they get married. Some women prefer to keep their surname and use the title Ms.

In formal contexts, we sometimes use Master for boys and Miss for girls. Miss also indicates single status (not married). The use of Miss is becoming less common among younger women, and Master now sounds old-fashioned.