Modals of obligation / recommentation
You have to study hard to pass your exams. (Strong recommendation)
You must study irregular verbs for next Monday. (Strong recommendation)
You should read newspapers, magazines and watch movies in original version. (Recommendation)
You shouldn't wait until the last moment to study. (recommendation)
You don't have to speak with an English accent to be understood. (No obligation)
You mustn't copy the final essay from the internet. (Not allowed)
Do we have to do this? (Obligation) /Must we do this? (Formal)
Ex: you mustn't use a dictionary. (It's not allowed/ don't do it).
Ex: you don't have to use a dictionary. (It's not necessary. The text is very easy).
Ex: you mustn't leave the class during the exam = you can't leave the class during the exam