Theory
Have to + infinitive: _________ obligation.
general
It's cold outside. I think he _________ wear a jacket.
should
Must + infinitive: _________ obligation.
personal
The kids from my brother's high school are really happy. They _________ wear a uniform anymore.
don't have to
Don't have to + infinitive: ___ obligation
no
The traffic light is red. You _________ cross the road.
mustn't
Mustn't + infinitive: it is _________
prohibited / forbidden / not allowed / ...
My watch is broken. I _________ buy a new one.
must
Should / shouldn't expresses:
She _________ take notes in this course. If she refuses, the teacher can give her a punishment.
has to