"We read you the newspapers."
Translation:Biz sana gazeteleri okuruz.
If you are speaking to more than one person, someone older than you who you are not close to, a stranger, or someone like your boss, you would use the siz form.
If you are talking to one person who you are close to, is similar to you in age, or is a friend/close family member, you would use the sen form.
"Biz" is the nominative case, so it's for subjects. "Bize" is the dative case, so it's for indirect objects (when the person who's being told something, given something, read something, etc.). For instance:
We read you the newspapers. = Biz sana gazeteleri okuruz. (We're reading them to you, so "biz" is the subject, and "sana" is the indirect object.)
You read us the newspapers. = Sen bize gazeteleri okursun. (You're reading them to us, so "sen" is the subject, and "bize" is the indirect object.)
It depends on what they were....? =) In the discussions, we can only see the English sentence and the primary Turkish translation, so I'm not sure which other translations you saw when you did the exercise. But if you were seeing both a "sana" option and a "size" option, yes: "size" is plural or formal "you," and "sana" is singular, informal "you."
If it's a specific and plural direct object (like the newspapers in this sentence), you use the accusative with a plural ending. Hence: "biz sana gazeteleri okuruz."
In the case of a general direct object, though, you don't use the plural ending or the accusative ending. For example, "we read you newspapers" (general "newspapers" with no "the") would be "biz sana gazete okuruz."
"Sana" is used when we're talking to one person that we know well, or who is significantly younger than us. For example, if we're reading to a child.
"Size" is used when we are talking to more than one person (even if they're young children) or to someone we're speaking formally with (such as elders, bosses, teachers, strangers, etc.)
Hope that helps :-)