Sometimes the SUBJECT of a sentence is not the one who acts (or does the action specified by the verb). In such a case, consider the subject to be PASSIVE; another person or thing will do the action of the verb.

In the passive voice, the one who does the action is called the AGENT.

Note that in the two sentences above, the event is the same. The difference in voice is merely who the writer or speaker has chosen to use as the subject of the action. The choice of voice does not alter the features of the event.