Passive voice in English

1. The passive of an active clause is formed by:

a) replacing the active construction by the construction of the auxiliary to be + the past participle of the active verb.
b) making the object of the active clause the subject of the passive clause
Active: They greeted him.
Passive: He was greeted.

The subject of the active clause can become the agent of the passive clause
He was greeted by the delegation.

However, in most passive clauses the agent is omitted
The fact is widely known.

The passive auxiliary be can sometimes be replaced by get (in informal style)
He got injured.