In the passive voice, the noun that would be the object of an active sentence appears as the subject of a sentence with passive voice, so, the action described by the verb is being done to the subject by an agent.
Examples:
1. John read the book in one week. (active)
The book was read by John in one week. (passive)
2. Mike buys a car. (active)
A car is bought by Mike. (passive)
