An adverb describes a verb or tells how an action is done. Adverbs usually tell when, where, how, or how often.
Yesterday I met a whale.
(The adverb yesterday describes when I met the whale.)
The whale floated calmly on the water.
(The adverb calmly describes how the whale floated.)
I bobbed nearby on an inner tube.
(The adverb nearby describes where I bobbed.)
I happily read her a story.