An adjective is a word or set of words that modifies (i.e., describes) a noun or pronoun. Adjectives may come before the word they modify.
That is a cute puppy. (describes the puppy)
She likes a high school senior. (describes the person)
Adjectives may also follow the word they modify:
That puppy looks cute.
The technology is state-of-the-art.
An adverb is a word or set of words that modifies verbs, adjectives, or other adverbs.
He speaks slowly (modifies the verb speaks)
He is especially clever (modifies the adjective clever)
He speaks all too slowly (modifies the adverb slowly)
An adverb answers how, when, where, or to what extent—how often or how much (e.g., daily, completely).
He speaks slowly (answers the question how)
He speaks very slowly (answers the question how slowly)