We use must when we believe something is necessary:
It’s a great book, you must read it
I must call my parents tonight
You must come over for dinner
We use have to when we are obliged to do something, even if we don’t
want to do it.
I have to get up early for work tomorrow
I have to complete my tax return before Friday
Do I have to?
When something is not permitted, we use mustn’t:
You mustn’t smoke here, it’s forbidden
It’s a secret, you mustn’t tell anyone
Don’t have to
Don’t have to is not the same as mustn’t