The verb “to be” serves three primary functions. First, it is used as a main verb to indicate existence. Second, it is used as a helper verb along with another verb in the -ing form to indicate a progressive tense. Third, it is used to indicate the passive voice in various tenses.
Main verb: I am certain that you are correct, although he is not convinced. The paper was good and the results were conclusive.
Progressive: I am going to the store. We were planning to have a party.
Passive: The paper was written. The paper is published. The paper will be written. The paper is going to be written.