should / can / have to / must (Modals of Obligation and Prohibition)

Should: tavsiye, öneri, “it is a good idea”

Shouldn’t : tavsiye etmememek, önermemek “ it is not a good idea” “it is a bad idea”

Can : izin “it is possible for you”

Can't: izin vermemek “it is not possible for you” "you are not allowed" "it is not allowed"

Have to : zorunluluk “ you need to” “it is necessary for you”

Don’t have to : zorunluluğun ortadan kalkması. Yapıp yapmamak sana kalmış “ it is not necessary” “you don’t need to”
Must: zorunluluk (çoğunlukla kişinin kendi isteğiyle oluşturduğu zorunluluk "I need to” “it is necessary for me”
Mustn't: izin vermemek (can't ile aynı anlamda) “it is not possible for you” "you are not allowed" "it is not allowed"

EX:

1.       It is a good idea to stay at home when you are ill.

You should stay at home when you are ill.

2.       It isn’t a good idea to walk in the rain without your umbrella.

You shouldn’t walk in the rain without your umbrella

3.       Is it possible for me to eat in the classroom?

Can I eat in the classroom?

4.       It isn’t possible for you to go out at night.

You can’t go out at night.
You mustn't go out at night

5.       It is necessary for you to finish your work today.

You have to finish your work today.

6.       It isn’t necessary to wear a uniform at this school.

You don’t have to wear a uniform at this school.

7.       It is necessary for me to stop smoking. 
I must stop smoking.