Have to/must + V1
You have to wear a seatbelt.
We must be on time for the test today.
Past and future forms of have to:
had to, will have to
I had to pay a fine for exceeding the speed limit.
All the employees will have to attend a 2-week management course.
a) There is a slight difference in the way must and have to are used.
Have to is used to express general, external obligations coming from someone, e.g. rules and laws:
We have to wear a uniform at work.
Must is used for specific (i.e. on one occasion) or personal obligations coming from the speaker:
I must finish the project tomorrow.
We must help our parents.
b) Have to is more common in questions than must:
Why do we always have to work overtime?
c) Have got to can be used instead of have to in colloquial English:
I’ve got to call my mom now.
can’t/mustn’t/be not allowed to + V1
You mustn’t use your phone until you get off the plane.
You can’t smoke here.
You’re not allowed to park here.
Don’t/doesn’t have to/need to
You don’t have to pay for the exhibition – it’s free.
We don’t need to hurry, we have plenty of time.
Didn’t have to/need to
You didn’t have to phone there yesterday.