Build any number up to 1,000.
21: 二十一 · èr shí yī — two tens and one.
105: 一百零五 · yī bǎi líng wǔ — 零 fills the missing tens place.
110: 一百一十 · yī bǎi yī shí — keep the 一 before 十 here.
1,000: 一千 · yī qiān — one thousand.
Pinyin uses dictionary tones. 一 can change tone in natural speech. 二百 and 两百 can both mean 200.