thank you all..

When first learning this sentence "I am fine/good." people usually use 是 [ shi4 ] for the verb "to be" (am/are/is) but 是 [ shi4 ] is only used to connect nouns, when connecting a noun with an adjective like in your sentence you need an adverb. Usually that is 很 [ hen3 ] which has the meaning of "very" but sometimes that meaning is not strong because this word is just used to fill the sentence, so rather than meaning "I am very good." it could just be "I am OK." To definitely express "very" you could use a stronger word like 非常 [ fei1 chang2 ]. In negative sentences, the adverb is 不 [ bu4 ] "not".

很→very.