Here is a very basic explanation about adverbs. An adverb is a word that modifies a verb, an adjective, or another adverb. For example: "I eat" is a sentence with a subject (I) and a verb (eat). But I can also say, "I eat slowly". The word "slowly" is an adverb. The adverb "slowly" modifies the verb "eat". That is, the adverb tells you how I eat: slowly. "She is pretty" is a sentence with a subject (She), verb (is), and adjective (pretty). But I can also say, "She is very pretty." The word "very" is an adverb. It modifies the adjective "pretty". The addition of the word "very" tells us she is not just pretty; she is pretty to a high degree. "He runs fast" is a sentence with a noun (He), a verb (runs), and an adverb (fast). But we can also say, "He runs extremely fast". The adverb "extremely" is an adverb which modifies the adverb "fast". The addition of the adverb "extremely" tells us that he runs not only fast, but very much faster than a typical runner.