The subject is the doer and the direct object is the receiver of the action. Transitive passive verbs have the subject receiving the action with the doer in a prepositional phrase or omitted in the sentence. The ball was kicked by the boy. The ball was kicked hard. The verb in the transitive passive voice always has is, am, are, was, were, be, being, or been as an auxiliary or helping verb.
Intransitive verbs have no receiver of the action.
They are classified as intransitive complete or intransitive linking. Intransitive linking are sentences with a predicate nominative or predicate adjective. The girl is Mary. The girl is cute. Intransitive complete are all the verbs that don't fit one of the other kinds of transitive or intransitive verbs.