Should is an auxiliary (modal) verb. It is primarily used to give advice/suggestion, while asking a question or while making predictions.
You should carry an umbrella today.
Should we invite Ben to the party?
If you take the train, you should be there in an hour.
The parcel should arrive in two days.
We use should have + -ed is used to express regret.
I should have studied harder when I was in school.
He should have made a card for his mother on her birthday.