You are supposed to do = You should do
be supposed to 相当于一个情态动词,过去式要变形,现在时和将来时用原形举一个例子好么，谢谢You are supposed to finish the job within the time limit.你应该在时间限期内完成工作（指现在也可，将来也可，因此现在没有完成工作呢）You are supposed not to make the same mistakes again in future.今后你应该不要再犯同样的错误（将来）I was supposed to go with them, but I was ill.我本来应该和他们一起去的，但我病了（结果没有去）