Adverbs modify or describe verbs, adjectives or other adverbs.
When, where, how or to what extent?
Ex: The boy walked slowly. How did the boy walk? Slowly adverb
Ex: The boy walked whenever he wanted to.
Modifies walked and answers when did he walk.
Adjectives modify or describe nouns or pronouns.
How many, what kind, how much, which one?
Ex: The cute girl is gone. Which girl? The cute girl. Cute is the adjective.
Ex: My friend who is sweet is going to the movies with my brother.
who is sweet -adjective phrase it answers which friend?