Modals or modal auxilaries are helpful verbs we add to express certain things, like obligation, permission or prohibition. In Dutch we call them: 'hulpwerkwoorden'
You probably already know these verbs, but maybe not when we have to use them. Have a look:
I must drive on the left in England
We have to get out of the museum before it closes at 5 pm
You should try a call your mum, she is probably worried.
We ought to go home early today.
Could I borrow a pen, miss?
You may leave the classroom early.
You can't go in there, all the walls have just been painted!