Here's why:
* Adverbs describe verbs, adjectives, or other adverbs. They answer questions like:
* How? (joyfully)
* When? (quickly, later)
* Where? (here, there)
* To what extent? (very, extremely)
In a sentence, "joyfully" would modify a verb, showing how the action is performed.
Example:
* She sang joyfully.
* The children danced joyfully.