No, there are two types of verb prefixes, separable and non-separable. vor- is a separable prefix, which means that in sentences where the verb is in the second position (like usual when it's the main verb) or the first position (like in questions), the prefix comes off and goes at the end.
vorlesen = to read aloud
Ich lese das Buch vor = I read the book aloud
Ich will das Bach vorlesen = I want to read the book aloud
Google translates them as:
Sie lesen mir ein Buch You read me a book
Sie lesen mir ein Buch vor They read me a book
This confuses me a lot. First, I thought the first translation should have been They instead of You. But then how does one use the formal You.
Second, how did vor at the end cause conversion from you to they. Is it correct?
They aren't glossing the "vor" correctly. Hovering over the word with the cursor indicates that the translation is "for". If it isn't a preposition here (which is a dirty trick to include in a section on prepositions) then they should explain that it's actually a verb prefix when you hover over it with the cursor.
The funny thing is that lead can be either "led" or "leed" depending on whether it's a verb or noun, so you're question is ambiguous.
But if you're asking whether this is present or past tense of "to read", the answer is it's present tense. The past tense would be "Sie lasen mir ein Buch vor" or (present perfect) "Sie haben mir ein Buch vorgelesen."
You just need to learn which verbs have separable prefixes and which ones don't. You will get to recognise the prefixes which are separable, (although some can be either separable or inseparable depending on the verb). There are quite a lot of them and many verbs that contain them:
No, They read a book to me.
But I agree with @mazinsweis: it can also mean You read a book to me. (If Sie is the first word of the sentence, you can't tell if it means "you (formal)" or "they".)