In English, there are three translations for the Dutch word 'moeten'.
These different translations are used in different contexts:
Must:
If you come up with a rule, that someone else has to follow, you use the word 'must'. It's not a general rule, but a rule you've thought of and your 'subjects' should listen:
Example:
You want to go out and you ask your parent for permission. You parents agree, but they have the following rule:
You must be home by eleven o'clock.
Since this rule doesn't apply to everyone in the world, and your parents came up with this rule, they use the word 'must'. It can also be used by teachers whi give their students homework, for example: you must finish your homework!
Have to:
If you want to tell your friends about the rule, it slightly changes. It's not a rule you thought of yourself; but it is a rule you have to follow. So in case of going out; you'd say:
I have to be home by eleven o'clock.
You express the rule you have to follow, yet you didn't make the rule yourself. Other examples are:
* You have to be quiet in a library. --> not your rule, but the library's rule.
* Everyone has to wear a seatbelt in the car. --> not your rule, but the government's rule.
Should:
Should is an advice. Someone may (strongly) advice you to do something, but there's no consequence if you do not follow the advice. As in; you would'nt get punsihed. If you compare this to the 'going out' example as stated under 'must' and 'have to', you'd say:
I think you should be home by eleven o'clock.
When the rule contains the words 'must' or 'have to', the rule comes with a concequence. in case of the word 'should', it's merely an advice, without concequences (no punishment).
Another example is:
You should see a doctor for that rash. --> advice. If the person doesn't go see a doctor, that's his/her own choice. being ill for a longer period of time is a concequence, but not a punishment given by the one who gave the advice.
You must be home by eleven. --> rule is made up by the parents, and so is the concequence. Not in time: grounded.
I have to be home by eleven. --> rule is still made up my parents, just like its concequence. You wouldn't give yourself a curvue and you most certainly wouldn't ground yourself.
I think you should be home by eleven --> still made up by someone else, yet there's no concequence (punishment) if you're going to be late.