have to and must are used for obligation

have to and must are used for obligation

Obligation
'Have to' and 'must' are both used to express obligation. There is a slight difference in the way that they are both used.
'Have to' shows that the obligation comes from someone else, not the speaker. This is usually referring to a rule or law.
We have to be at the airport at least two hours before the flight.
I have to work on Saturday.
They have to wear their uniforms at school.
'Must' shows us that the obligation comes from the speaker.
I must hand in my thesis by tomorrow.
I really must call my parents.

http://www.perfect-english-grammar.com/modal-verbs-of-obligation.html

https://linguapress.com/grammar/modal-obligation.htm

https://learnenglish.britishcouncil.org/en/quick-grammar/modals-1

http://www.myenglishpages.com/site_php_files/grammar-lesson-modals.php

https://www.slideshare.net/mobile/DavidMainwood/modals-for-obligation-and-prohibtion-9128360

https://youtu.be/j8jQpLf1WkY

https://youtu.be/ELfjg5n4xHE