1. The voice of the verb is distinct from its tense. Don't confuse the passive voice with the past tense. (Sentence 2 happens to be in the past tense, but 3 is not; both 2 and 3 are in the passive ...

This is the person or thing doing the verb. The passive voice is made with subject + to be + past participle + by + object. Note that the active voice object becomes the passive voice subject.