Adverbs are used to modify and provide more information about verbs, clauses, adjectives, and other adverbs. Adverbs can appear in different positions, such as modifying verbs like "grow rapidly" or adjectives like "extremely difficult." They can also modify other adverbs, as in the example "incredibly quickly." The document provides examples of adverbs modifying verbs, adjectives, and other adverbs to illustrate how adverbs are used to give additional information.