grammar terminology question

I am having trouble finding the correct grammar terminology to characterise some "question words".
here's a sample sentence:
"Many people think cricket is boring but when you understand how the game works it becomes addictive."
so, the question is what are the words "how" and "when" in this sentence?
the options are: nouns, adjectives, main verbs, auxillary verbs, modal verbs, adverbs, gerunds, definite articles, indefinite articles, conjunctions, determiners, pronouns or superlative adjectives?
can anyone help please?

[Tdol]

In that sentence, it's a conjunction.
In a question, it's an adverb.