In a sentence such as ‘She is young’, or ‘Chinese is difficult’, the Chinese adjective functions as the verb, and 是 shì (to be) is not used.

The word 很 hěn (very) must be used before the adjective, but it doesn’t have any meaning here.

她 很 年轻。

She is young.

Tā hěn niánqīng.

汉语 很 难。

Chinese is difficult.

Hànyǔ hěn nán.

我 很 忙。

I am busy.   

Wǒ hěn máng 。

Without 很 hěn，however, a comparison is implied.

汉语 难。 Chinese is difficult.（implying it is difficult than another subject or language.) Hànyǔ nán.

The word 很 hěn is also known as an intensifier. Other intensifiers can also be used with Chinese verb-adjectives.

If another intensifier is used, 很 hěn is no longer needed.

房子 特别 漂亮。 The house is particularly beautiful. Fangzi tè bié piāo liàng.