The noun 女孩 (nǚhái) means "girl" and refers to a young female person. It can be modified by adjectives using the particle 的, as in 漂亮的小女孩 (a beautiful little girl).
那个女孩是我的同学。
Nàge nǚhái shì wǒ de tóngxué.
That girl is my classmate.
对面走过来一个小女孩。
Duìmiàn zǒu guòlái yī ge xiǎo nǚhái.
A little girl came walking from the other side.
这个女孩钢琴弹得很好。
Zhège nǚhái gāngqín tán de hěn hǎo.
This girl plays the piano very well.