Form
positive statement ->question tag negative - You are Tom, aren't you?
negative statement->question tag positive - He isn't Joe, is he?
Examples
with auxiliaries
You've got a car, haven't you?
without auxiliaries (use: don't, doesn't, didn't)
They play football on Sundays, don't they?
She plays football on Sundays, doesn't she?
They played football on Sundays, didn't they?
Questions tags are used to keep a conversation going. You can agree or refuse to a sentence with a question tag.
You go to school, don't you?
You agree. You refuse.
Yes, I do. No, I don't.
You aren't from Germany, are you?
You agree. You refuse.
No, I'm not. Yes, I am.