In order to express the idea of obligation, to talk about rules, duties, or orders, to give strong advice to other people or to ourselves, must, have (got) to, should and ought to are used.

Should and ought to are used when a speaker thinks it is a good thing or right that a person does something. It indicates that a person has a duty to do something.

Must is used to order someone to do something, while have to means that there is a rule that forces that person to do something.

Must, have (got) to or simply need to is used when it is necessary to do something.