What's the difference between a past tense verb and passive verb? I'm a bit confused.
The past tense is used to talk about what has already happened.
The passive voice is used when you want to emphasise what an action is done to, rather than what has done the action (active).
The past tense is used when you want to talk about something that has already happened. There are two main categories in the past tense: perfect and imperfect. The perfect is sentences like
I have gone
you have been
we have seen
they have lent
which use an auxiliary verb (have) and a past participle (gone, been, seen, lent).
The imperfect uses only one verb, which is the imperfect conjugation of the verb. For example,
Here there is no auxiliary verb, and rather than the past participle it uses the imperfect conjugation of the verb (went, were, saw, lent), although in some cases (lent), the past participle and imperfect conjugation are the same.
The passive voice is something different entirely. The passive is used when what is usually the object of the sentence is made the passive subject. It is contrasted to the active. For example,
active: I threw the book
passive: the book was thrown (by me)
active: he opened the window
passive: the window was opened (by him)
You can see how the active emphasises the doer of the action, while the passive emphasises the what it is done to.
Overall, past and passive are completely different, even if they have similar names. The past tense is used to talk about what has already happened, and the passive voice is used to emphasise what it has happened to.