What is the job of adverb? Is it used to modify a verb or what? Please explain.
Similar to how you can use an adjective to add more information about a specific noun (for example, "the tall boy", rather than just "the boy"), you can use adverbs to add more information and describe a specific verb. For example, you could say that someone shut a door, but that doesn't give the same meaning as saying someone shut the door furiously. The word "furiously" adds more information and describes the verb "shut".
Adverbs can also describe other adverbs, as well as adjectives. For describing adjectives, you could say that a giant is extremely big, rather than just saying the giant is big. Similarly, you can use adverbs to describe other adverbs, using a word such as "very". Using our example from before, one could say that someone shut the door very furiously, rather than just furiously.