1
This indicates that there is no obligation to do this action, it is not required, but you can do it if you want
2
This modal verb is used to express obligation, necessity or daily responsibilities but it refers to an external obligation. It's less formal
3
This is used to express needs, requirements and necessities , but it indicates that it is not urgent as 'must' and 'have to'
4
This indicates that this action is forbidden or prohibited. Not allowed
5
This modal verb suggests a recommendation, advice, or expectation, indicating something that is desirable or advisable to do.
6
This modal verb indicates strong personal obligation and it is used in written rules and instructions. It is more formal
