active and passive voice

What do you mean voice?

In English grammar, voice doesn't mean the sound you make when you speak. It shows whether the subject of a sentence is doing the action, or having the action done to it.
If the subject is the person performing the action, we use the active voice.
When we're not bothered about who or what carried out the action of the verb ,we use the passive voice. In other words, the subject of the sentence refers to someone or something who does not perform the action but is affected by the action of the verb.

Active Voice	Passive Voice
I cleaned the office while you were out.	The office was cleaned while you were out.
Paris Hilton switched on the Christmas lights.	The lights were switched on

 
We say things in the active voice when we want to show who or what has done something.
In the active voice the agent (the person or thing that does something) is the subject of the sentence.

For example:
"She cleaned the office." (Who cleaned the office? She did=the subject)
"He crashed into my car." (Who crashed into my car? He did=the subject)

The active voice uses fewer words than the passive voice.
The passive voice is used when the subject of a sentence is the person or thing affected by the action of the sentence.
The passive voice may use any tense of the verb to be:-

to be		past participle
is / are / am was / were	(present simple) (past simple)	finished.
is being / are being /am being was being / were being	(present continuous) (past continuous)	cleaned.
has been / have been had been	(present perfect) (past perfect)	sent.
will be	(future)	tired.

We particularly use the passive voice when we don't know or aren't bothered exactly who has done something. This is called passive without agent where the recipient of the action becomes the subject.

For example:
"The office was cleaned." (What was cleaned? - The office=the subject)

We often use the passive to report what someone has said, but we want to avoid telling anyone who said it.

For example:
"I was told you weren't coming."

Sometimes it is used in order to deliberately avoid saying who did something, or more often who's to blame for something. Either because you don't know, or because you don't want to say. You'll often see it used in politics, the business world, or in any other activity involving bureaucracy.
"The civilian was shot." (Who was shot? The civilian=the subject)
"The report was mislaid." (What was mislaid? The report =the subject)
Sometimes you may want to use the passive voice but wish to mention who carried out the action. This is called passive with agent and the agent is usually introduced with the word by.

For example:
"The office was cleaned by Mrs Smith."

Or you may use a subject such as people, someone, they etc, when you don't know who the agent is.

For example:
"The car was stolen by joyriders."

Be warned though, the passive voice can sound pompous or evasive.

When you can't use the passive

Intransitive verbs cannot be used in the passive. This is because they cannot have objects, and so there is nothing to become the subject of the passive sentence. For example with verbs like die or arrive.