BE SUPPOSED TO
It has three different meanings:
It is supposed to = it is said to...
I'm going to buy
his book. It's suposed to be
very good ( it is said to be very good)
Why hasn't the teacher come to school today? She is supposed to be ill (She is said to be ill)
Something that is supposed to happen= it is planned , arranged or expected. Often this is different from what really happens
was supposed to start
at 10.00 sharp but the teacher was late
I'm supposed to give a conference in Berlin tomorrow but I think I'm going down with flu.
You are not supposed to do something= it is not allowed or advisable for you to do that
She is not supposed to speak Spanish in an English class.