Passive Voice

The rule is be + past participle.

Present Simple
He repairs the car.
The car is repaired.
Past Simple
He repaired the car.
The car was repaired.

Present Continuous

He is repairing the cars.

The cars are being repaired.

Past Continuous

John and Fred were repairing the cars.

The cars were being repaired by John and Fred.

Future "will"
Jess will repair the car.
The car will be repaired by Jess.
Future "Be going to"
They are going to repair the car.
The car is going to be repaired.
Present Perfect
He has repaired the car.
The car has been repaired.
Past Perfect
She had repaired the car.
The car had been repaired.
Modal
They should repair the car.
The car should be repaired.

More information in: Post of 18th November 2009