The word ‘must’ is used with verb to show compulsion . Some examples are given here in the form of affirmative, negative and interrogative sentences.
Have a look-
Sam must send a mail.
Must Sam send a mail?
Sam must not send a mail.
Must Sam not send a mail?
My sister must go.
Must my sister go?
My sister must not go.
Must my sister not go?
Students must obey their teachers.
Must students obey their teachers?
Students must not obey their teachers.
Must students not obey their teachers?
Players must play honestly.
Must players play honestly?
Players must not play honestly.
Must players not play honestly?