- You can't turn right here. You have to turn left.
- I have to wear glasses for reading.
- George can't come out with us this evening. He has to work late..
We use do /does/did in questions and negative sentences (for the present and past simple):
- What do I have to do to get a new driving licence? (not What have I to do?)
- Karen doesn't have to work Saturday. (not Karen hasn't to)
- Why did you have to leave early?
Must is similar to have to:
- It's later than I thought. I must go. or I have to go.
You can use must to give your own opinion (for example, to say what you think is necessary, or to recommend someone to do something). Have to is also possible:
- I haven't spoken to Sue for ages. I must phone her. (= I say this is necessary)
- Mark is a really nice person. You must meet him. (I recommend this)
You cannot use must to talk about the past:
- We had to leave early. (not we must)