I can't figure out if the grammatial classification for the word "how" when it starts a question.

In a copula it refers to the complement... so it should be an interrogative adjective, like in the sentence "How are you? I am fine".

But in a "real" sentence it usually refers to and adeverb, like in "How did he do in scholl? He did well"... so here it would be working like an interrogative adverb.

Can someone help me with this.
Thank you.
isn't "adverb" just a catch-all category they throw all and sundry into?
The word 'how' always works as an adverb.
 suzi's reply was promoted to an answer.