Must, Have got to, and have to express a need to do a certain action.
Must is considered to be more formal whereas, have to is considered to be more informal.
Have to is more commonly used in everyday american speech.
1. I have to study tonight.
2. All employees must wash their hands.
3. I have to (haf-to) clean my room.
4. You must clean your room before you go.
5. You have got to pay that bill today.