grammar - Generalised rule for verb usage in simple present tense using participle

I'm doing a school exercise where I have to give an explanation of the underlined (or in this case bold) verb usage in given sentences, following this format:

I was waiting.

past continuous (or progressive) =
subject + was / were + verb + ‘-ing’ (or present participle)

The last sentence I am to anaylse is giving me trouble:

Toyota cars are made in Japan.

I've indentified the tense as present simple, and cars is clearly the subject, and "are" at least one of the verbs. But what is the rule for past participles in simple present tense? I've done fairly extensive searches online and found grammar websites that give examples of the same format as present simple tense, but none that give any explanation or rule for how the past participle is used in this case.

My best guess for the desired analysis is:

cars are made

Simple present =
subject + is / are + past participle

But this is only an inference, and I don't know if it accurately reflects any actual grammatical rule.

Any help will be appreciated. (And don't worry, I'm allowed to use the internet, several links are even included with the exercise, so you're not helping me cheat)