Be supposed to is a very common English phrase. It has a few different uses, so let's look at the different ways we can use this phrase in conversation.
Be supposed to is used to mean "it is said" or "it is believed." For example:
◆ The food at that new restaurant is supposed to be really delicious.
◆ Hawaii is supposed to be a lovely place for a honeymoon.
◆ This temple is supposed to have been built in the 14th century.
Be supposed to is often used to talk about things that should happen. It means the same as "should," "expect" or "have to."
◆ I am supposed to wear a suit at work. = I have to wear a suit.
◆ We are supposed to get a bonus in July. = I expect to get a bonus.
◆ I am supposed to get to the station by noon tomorrow.
=I should get to the station by 12.
In spoken English, be supposed to can also be used to show that the action does not really happen. In this case, we stress the word supposed to show that the action didn't happen.
◆ I am SUPPOSED to turn off the lights when I leave the room. (But I don't)
◆ I was SUPPOSED to leave the house before 9 o'clock. (But I overslept)
◆ We are not SUPPOSED to eat at our desks. (But we do)