Obligation Must-Have to
You must pass your exam = You have to be pass your exam
I will have to wear a crash helmet to drive a motorcycle.
Helen didn't need to work every day.
I need to study very hard to pass my exams.
In spain you mustn't drive on the left.
You work very hard. you should rest more.
Today is my mother birthday, I had better buy a present.
Ability and knowledge
Mary can speak italian.
She could drive three years ago