Adverbs can tell you more about a verb, like this:

Mike battled bravely.

battled is a verb describing an action.

bravely is an adverb telling you more about how the action was carried out.

Adverbs can tell you more about another describing word, like this:

Mike was really annoyed.

annoyed is a describing word telling you more about Mike.

really is an adverb making the describing word stronger in meaning.

The boys were behaving very badly.

badly is an adverb telling you how the boys were behaving.

very is another adverb, adding to the meaning of badly.