Active voice: The voter has cast the vote.
Passive voice: The vote has been cast by the voter.
In a sentence using active voice, the subject of the sentence performs the action expressed by the verb.
The voter has cast the vote.
The subject, voter, cast, or placed, the vote.
Here's another example of active voice: The girl rode her bike.
In a sentence using passive voice, the subject is acted upon or receives the action expressed by the verb.
The vote has been cast by the voter.
The subject, vote, receives the action of being cast by the voter.
Here's another example of passive voice: The boat was driven by the tall boy.
Active voice is generally considered more direct and concise but passive voice is often used in scientific or scholarly writing.