Note that all subjects take the same form of the modal.
Subject + Modal + Base Form of Verb + Objects
He can play the piano.
I must leave soon.
Subject + Modal + Not + Base Form of Verb + Objects
They can't visit next week.
You shouldn't go to that film.
Modal + Subject + Base Form of Verb + Objects
Can you help me?
What should I do?
Giving Advice with Should
'Should' is used when asking for or giving advice. It is also used when asking for suggestions.
I think you should see a doctor.
What type of job should I get?
Expressing Ability with Can
'Can' is used to speak abilities.
He can speak Japanese.
Can you play golf?
Asking for Permission with May
'May' is used to ask for permission.
May I help you?
May I visit you this afternoon?
NOTE: In spoken English, 'Can I ...?' is often used instead of 'May I ...?'
Test your understanding with this short quiz.