1.
to be expected or required to do / be sth according to a rule, a custom, an arrangement, etc. :
You're supposed to buy a ticket, but not many people do.
I thought we were supposed to be paid today.
The engine doesn't sound like it's supposed to.
You were supposed to be here an hour ago!
How was I supposed to know you were waiting for me?
'Yes and no.' ' What is that supposed to mean ?' (= showing that you are annoyed)
2.
to be generally believed or expected to be / do sth :
I haven't seen it myself, but it's supposed to be a great movie.