use the auxiliary verb “be” with the past participle.
use the expression “by”, to show who or what does the action.
are used in a variety of tenses.
can be used with modals.
use “it” to introduce a clause as the subject.
For example, “It is believed that education is important.”
cannot be used with intransitive verbs. (Intransitive verbs have no object, for example, “die”, “arrive”, “sleep”.)
usually do not have infinitives as subjects.
For example, “Maude wants to see the movie” (active sentence); “To see the movie was wanted by Maude” (not possible in passive form).