We use SHOULD....
to give opinion/to say what you think
"Everybody should do some exercise regularly."
"You shouldn't worry so much for little things."
to talk about probability
"We should be there in about 20 minutes."
"It should be easy for you to make friends there."
to give advice
"What should I do?"
"You should speak with him about this problem."
"He shouldn't be late this time."
to criticise past decisions
"You should have left earlier."
"You should have sent an sms yesterday."