This explain how is formed the Passive Voice.

1. PASSIVE VOICE
Passive Voice is used when the object is on the
action, who performing the action.
Example: They eat chickens – Chickens are eaten.
The object of the active sentence becomes the
subject of passive sentence.

2. 
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We make the passive putting the verb to be into
whatever tense and then adding a past
participle.
For regular verbs, we make the past participle
adding -ed to the infinitive.
You can use the passive form if you think that the
thing receiving the action is more important or
should be emphasized.
The passive voice is used if you don't know is
doing the action or if you don't want to mention
who is doing the action.

3. EXAMPLES
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Present simple: I make a cake – A cake is made.
Present continuous: I am making a te. - A te is
being made.
Past simple: I eat a cake – A cake was eaten.
Past continuous: I was drinking a beer – A beer
was being drunk.
Present perfect: I have felt a noise – A noise has
been felt.
Present perfect continuous: I have been feeling a
noise – A noise has been being felt.
Past perfect: I had made a juice – A juice had
been made.

4. MORE EXAMPLES
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Future simple: I will drink a coffee – A coffee will
be drunk.
Future perfect: I will have drink a coffee. - A
coffee will have been drunk.