Should, ought , have to and must

Should and ought are very similar. They are both used to talk about obligation and duty, to give advice; and to make a suggestion about something

You ought to/ should  read The Secret . It s a great book. (a suggestion)

You ought to/ should  drive more carefully. (an advice)

*Must and have to are much stronger than should and ought to. 

It is used to talk about something is necessary or required

You must bring your homework tomorrow.

We can give advice with should and ought to.

We can give orders with must and have to.

e.g.

you ought to give up smoking. (an advice)

the doctor said you must give up smoking. (an order)

*We use  don't have and doesn’t have for something that is not necessary.

You don't have to come to the party at 6. Come at any time.

She doesn't have to finish her homework now.