hyphenated noun

Hi,
I wonder what I need to conceptualize better what is involved in the use of a hyphento denote one aggregate noun.

possible instruction in a language game:

Let's play a "wh" game with wh-words.

At first, I think I can see why the word "wh-words" in linked with a hyphen and when the word "wh" is in quotation marks, but this knowledge is elusive. Sometimes, I think I get it and sometimes, I don't.

How about this?

She is a teacher-student.

I think I can see why it has been made a noun where two seemingly unlikely nouns are held together by a hyphen to form an aggregate noun (if I can call it that), but a clear explanation is escapiing me. Can you tell me what your explanation is for this kind of situation (if I have made it clear).