Traditional grammars describe adverb clauses as dependent or subordinate clauses that consist of a subordinating conjunction followed by a clause and that perform an adverbial function.
Grammatical Form of English Adverb Clauses explains the internal structures that distinguish adverb clauses from other grammatical forms.
Grammatical Function of English Adverb Clauses explains the only grammatical function of adverb clauses in English grammar.
Using Adverb Clauses as Adjunct Adverbials exemplifies adverb clauses performing the grammatical function of adjunct adverbial.
For information on adverb clauses, see English Adverbs.