Necessary/Very important to must
have/has to
I must finish this before I go home.
You have to show your passport at the border.
Important not to
mustn’t
don’t
You mustn’t be rude to the customers.
Don’t spend more than the budget.
Not necessary
don’t have to
doesn’t have to
We don’t have to work overtime.
Good idea to
should
You should check your emails before you send them.
Not a good idea to
shouldn’t
We shouldn’t increase our prices.
Possible to
can
You can use my office if you want.
Not possible to
can’t
You can’t park here.