Good morning, Englishquestion.
(1) Yes, many times it means that we think something is true:
It's 10 p.m. in New York. My grandmother must be sleeping now.
You have been accepted as a student to the university. You must be very happy.
(2) Sometimes it means something like "should" or "have to":
When you enter a church, you must be quiet.
When you see a yellow traffic light, you must be ready to stop your car.
When you speak with a teacher, you must be respectful.
Have a nice day!
Student or Learner