My mother was a teacher. She was also really into psychology, to get her kids to perform. One of her favorite methods was to use passive voice, because it didn't sound as bossy to the intended victim...um...student. She'd also use this method at home. So instead of telling us to 'take out the trash,' she'd say, 'the trash needs to be taken out.' It sounded the same to us because if we didn't do what she wanted, she'd get angry. I didn't want to be on the punishment end of her anger, even if she was trying to sound less bossy.
So what is passive voice? When I was younger, the high school was selling old books from their library. I bought one that's entitled 'English Grammar and Composition' by John Warriner, Mary Whitten, and Francis Griffith. Even though Harcourt Brace Jovanovich published the thing in 1973, there's a wealth of information in this little book. Here's some of the information, partially paraphrased.
When the sentence is in active voice, the structure is the subject performing the action.
When the sentence is in passive voice, the subject receives the action.
Here's an example:
She shot him. Active. She is the subject, shot is the verb, and him is the object.
He was shot by her. Passive. He is now the subject. The verb is a verb phrase that includes a form of 'be' and the past participle of the verb. In this case, it's 'was shot'. 'By her' can now be omitted and the sentence still makes sense.
If other helping verbs appear in the active sentence, they must also be included in the passive. So, for example, 'Someone has yelled my name' is active. The passive version would be 'My name has been yelled.' 'Has' is in both sentences.
The passive voice puts the emphasis on the person or thing receiving the action rather than the one performing it. It is often used when the speaker doesn't want to say who did the action. Even so, it can be overused. A succession of passive sentences is considered weak and awkward and should be avoided.
Have a great day!
Reference: 'English Grammar and Composition' by John Warriner, Mary Whitten, and Francis Griffith. Harcourt Brace Jovanovich, New York, 1973. Passive voice--pages 142-144