More info can. can't, have to, don't have to, must and must not

Have to and must are used to indicate a rule or an obligation. They have almost the same meaning. Have to is often used to indicate the obligation comes from outside, eg I have to lose weight (the doctor told me). Must often shows an internal feeling, eg I must call my mother tonight.

Don't have to and must not (mustn't) are very different. Don't have to shows a lack of obligation / no rule eg you don't have to carry your umbrella when it rains (but you can if you want to). Mustn't indicates prohibition, the existence of a rule saying don't, eg you mustn't chew gum in class (if you do there will be some consequence).

Can shows permission, that something is possible or allowed. eg People in England candrink alcohol when they're 18.

	Alternatives	Past tense
must / have to		had to
don't have to	need not (needn't)	didn't have to
mustn't	can't	was not allowed to / couldn't
can	be allowed to	could / was allowed to

Complete the following with have to, don’t have to or mustn't.

You _________________ have a licence to drive a car.
You _________________ have a licence to ride a bicycle.
You _________________ tip waiters and taxi drivers in Japan.
You _________________ wear shoes inside your house in Japan.
Students _______________ go to school on Saturday in Japan.
Students _______________ go to school on Saturday in England.
Foreigners ______________ carry an ID card in Japan.
Policemen ______________ wear a uniform.
Passengers ________________ smoke on the subway.
Gardeners _______________ wear ties.

Taken from: http://english-the-international-language.com/rules.html