A clause that tells how, when, where, or to what extent something was done is a(n) _____.
adverb clause
http://grammar.about.com/od/ab/g/qdvclterm.htm
A clause that provides information about how, when, where, or to what extent something was done is called an adverbial clause. Adverbial clauses function as adverbs in a sentence, modifying verbs, adjectives, or other adverbs. They add more detail and describe the circumstances or conditions of an action, providing answers to questions such as how, when, where, or to what extent an action took place.
To identify an adverbial clause in a sentence, you can look for certain words or phrases that commonly introduce such clauses, such as "when," "where," "how," "since," "because," "although," "if," "unless," and so on. These subordinating conjunctions are often used to introduce adverbial clauses and connect them to the main clause of a sentence. Adverbial clauses can appear at the beginning, middle, or end of a sentence.