If we are told that we 'must' do something, like complete homework, the modal verb 'must' indicates a high level of modality. There is no argument. The homework has to be done. But if we are told ...

what you are supposed to do/what you should do/what you ought to do (It often means 'shall', eg shall/should I help you?) sollen to be supposed to, ought, should what you may do/what you are ...