You are probably familiar with the active voice, in which the subject does the action. E.g. "Lynnea usually cooks dinner." or "Axel finished the yard work yesterday."
In the passive voice the action is done to the subject. In the above sentences the verb takes a direct object (cooks takes dinner / finished takes yard work). In passive voice the object is turned into the subject, and the verb is formed with the verb "to be" and a past participle. E.g. "Dinner is usually cooked by Lynnea." or "The yard work was finished by Axel."
The rules for the use of the different tenses in the passive voice are the same as those for the active voice. The Present Simple is used for facts and repeated actions, the Past Simple for completed actions, etc. The difference is that the verb "to be" changes form to create the tenses and the main verb (or "action" verb) remains in the past participle form.
Here are examples of the major five tenses:
A passive changes the emphasis of a sentence. Usually in a passive the event or result is more important than the person who causes it to happen. Often the actor, as in the above sentences, is unknown or not important.
Although the active voice is considered the stronger form of expression and is used more often, the passive is common in certain styles of writing, such as scientific or legal documents.