must
You must stand in line!
You mustn't sit on the desk.
You must get up and get ready for school.
You mustn't eat anything until you see the doctor.
when,before,after
You should be quiet when you are in the reading room.
When I grow up,I'll be a nurse and look after patients.
I can't go out before Mum comes back.
After I cooded the food,I went to busy some flowers for Dad.
if
If you don't go soon,you'll be late.
If you are ill,you'll have to see the doctor.
If you don't want to go alone,I'll go with you