How do you explain what an adverb is?

An adverb is a modifying Word, that provides additional information about a verb, an adjective, or another adverb. Here are examples of one-Word adverbs modifying other Words:

He ran quickly. (the adverb modifies the verb ran - quickly tells how he ran)

The boy is extremely tired. (the adverb extremely modifies the adjective tired - he is very tired)

He threw the ball too far. (the adverb too modifies the adverb far - quite different from just far)