Adverb clauses are dependent clauses that modify verbs, adjectives or other adverbs. Usually, they modify verbs and are introduced by subordinate conjunctions such as after, although, because, since, if, so that, than, unless, until, when, where, while, before, because.
Example: They say he changes when the sun goes down
"When the sun goes down" is the adverb clause modifying the verb "changes" by telling when.