I would say that tag questions are short questions coming after a statement. They are used to confirm what was first said, to be sure of something as in the following sentence: you are single, aren't you? If the first sentence is afirmative, the tag question will be a negative; if the first one is negative then the second will be afirmative (she can drive, can't she? - she doesn't speak English, does she?). In sentences that do not have the auxiliary verb, the question is made by using it, like: He studies English, doesn't he? I also explain some special cases to my students as in :
1. Let's talk about business, shall we?
2. the imperative: Give me your hand, will you?
3. I am right, aren't I?
I hope to have helped.