An adverb clause is a group of words that functions like an adverb, providing information about when, where, why, how, or to what extent something happens. It usually begins with a subordinating conjunction, such as because, although, or when. For example, in the sentence "I will go to the park when it stops raining," the clause "when it stops raining" tells us when the action will occur. These clauses can be placed at the beginning or end of a sentence. They add depth to writing by explaining the circumstances surrounding the main action. For instance, "Although it was late, she finished her homework" uses the adverb clause "Although it was late" to explain the situation under which the action took place.