Must talks about something you think is necessary to do. It is your choice.
Have to talks about something that someone else thinks is necessary to do. It is not your choice.
- I must get my hair cut. I think that it is too long.
(My choice.) - I have to get my haircut. My girlfriend hates long hair.
(My girlfriend’s choice.)
Must is also used on public notices.
- All employees must carry their ID cards at all times.
(On a sign at a reception desk.)
