One of the most frequent jobs for an adverb to perform is to add information to the verb. In the sentence, "He shouted loudly to his friend", the verb is "shouted" and the adverb is "loudly". The word "loudly" modifies the verb.
Adverbs also modify adjectives and other adverbs. In the sentence, "She moved rather quickly", the adverb "quickly" adds some information to the verb, "moved". But she didn't just move "quickly", she moved "rather quickly". "Rather" is an adverb modifying, or adding information to, another adverb. In the sentence, "It was an extremely pleasant evening", the adjective "pleasant" is modified by the adverb "extremely". As you can see, adverbs are very adaptable and can be used to add all sorts of information to your writing. One tip which might help you spot some adverbs is that many of them end with the -ly suffix.