Passive: The mayor was informed of the accounting errors.
Active: Mr. Jones informed the mayor of the accounting errors. (adds clarity)
Active: The mayor was aware of the accounting errors. (adds responsibility)
In the passive voice, the actions are performed upon the subject by someone or something else.
When the subject is more important than the actor, the passive voice is a useful style.
Passive: The graduated cylinder was filled with 750 ml of the solution. (no actor)