An adjective modifies a noun or a pronoun by describing or identifying words. An adjective usually comes before the noun or the pronoun which it modifies. ("a nice cat" "a happy couple")

An adverb can modify a verb, an adjective, another adverb, a phrase, or a clause.
An adverb describes an action (verb) and answers questions such as "how," "when," "where," "how much". Many adverbs can be identified by their characteristic "ly" suffix (coldly, plainly, happily, etc.)

Unlike an adjective, an adverb can be found in various places within the sentence.