How do numbers work in Chinese?
一 yī 'one'
On its own pronounced yī. Before Tones 1-3 it is Tone 4, but Tone 4 it becomes Tone 2.
二 èr 'two'
But use liǎng before a measure word.
三 sān 'three'
四 sì 'four'
五 wǔ 'five'
六 liù 'six'
七 qī 'seven'
八 bā 'eight'
九 jiǔ 'nine'
十 shí 'ten'
For eleven, twelve etc. you say "ten one", "ten two" etc.:
十一 shíyī 'eleven'
十二 érshí 'twelve'
十三 shísān 'thirteen'
十四 shísì 'fourteen'
十五 shíwǔ 'fifteeen'
十六 shíliù 'sixteen'
十七 shíqī 'seventeen'
十八 shíbā 'eighteen'
十九 shíjiǔ 'nineteen'
This is easier than English (and much easier than Hindi that has different words for every number between one and a hundred!).
What about the tens?
You say "ten one", "ten two" etc.:
二十 érshí 'twenty'
三十 sānshí 'thirty'
四十 sìshí 'forty'
五十 wǔshí 'fity'
六十 liùshí 'sixty'
七十s qīshí 'seventy'
八十 bāshí 'eighty'
九十 jiǔshí 'ninety'
Beyond a hundred
一百 yìbǎi "a/one hundred"