Voice shows the relationship of the subject to the action of the verb.
There are two voices in English- active and passive.
The Active Voice
In an active voice sentence, the subject is the agent (the doer of the action) and the object of the sentence receives the action of the verb. The active voice is more commonly used than the passive.
The sentence structure in the active voice is: subject + verb + object
Becky ate an apple.
XXXBecky is the subject/doer of the action and apple is the direct object of the verb eat
The Passive Voice
In the passive voice, the subject of the sentence receives the action of the verb. The agent performing the action in a passive sentence may be identified with the phrase ‘by the…’ or the agent may be omitted entirely.
The sentence structure in the passive voice is: subject + auxiliary verb + past participle + agent
The apple was eaten by Becky.
XXXApple is the subject and receives the action of the verb eat, Becky is the agent
When changing a sentence from active to passive, the direct object in an active voice sentence becomes the subject in a passive voice sentence.
Harry Drove the car.
The car was driven by Harry.
Note: Not all verbs have a passive form. Verbs that do not have a direct object can not form the passive because there is nothing which could function as the subject.
For more information about the voice take a look at
An explanation of the active and passive voice in English and how to change voice– www.understandinggrammar.com