Learn the difference between ‘must’ and ‘don’t have to’ with English In A Minute from BBC Learning English.
QUIZ: Which sentence means that students are not allowed to wear trainers at school?
A) Students mustn’t wear trainers at school.
B) Students don’t have to wear trainers at school.
You’ll find the answer, a summary and more questions here: https://www.bbc.co.uk/learningenglish/english/course/eiam/unit-1/session-10