An adverb is a word that modifies a verb, an adjective, or another adverb. Adverbs generally answer one of four questions: how, when, where, or to what extent.
Adding the suffix -ly to an adjective commonly turns the word into an adverb.
Examples: He ran fast. (how)
He responded immediately. (when)
He put it there. (where)
He became extremely happy. (to what extent, modifies adjective)