Have to is the same as must. It implies that you don’t have a choice.
John has to go to work everyday.
The students have to study tonight.
To be supposed to means an obligation. It is something that you should do, or something that another person expects you to do. Don’t forget to use the verb be in front of supposed to.
Sally is supposed to meet her friend tonight.
All of the employees are supposed to attend today’s meeting.
Ought to means a suggestion. You should do something but you don’t have to do it.
We ought to clean the house tonight.
Phillip ought to help you with your homework.