SINO-KOREAN NUMBERS

0 → 영   1 → 일   2 → 이   3 → 삼   4 → 사   5 → 오   6 → 육   7 → 칠   8  → 팔   9 → 구 

They're used for telephone numbers, subway or bus lines, addresses, building floors, years, minutes, seconds, page numbers, weight, height, temperature, and dates. 

10 → 십

To make numbers like 20, 30, 40, etc you'll only need to put the unit (two, three, four, etc) before "십", so they will be 이십, 삼십, 사십, etc. 

Then, to make all the numbers until 99, you'll just put the unit you need after 십.

Eg: 27 → 이십질   34 → 삼십사   58 → 오십팔   77 → 질십질

100 → 백

As you would do with 십, to make numbers like 200, 300, 400, etc you'll only need to put the unit (two, three, four, etc) before 백, so they will be 이백, 삼백, 사백, etc.

Then, to make all the numbers until 999, you'll just put the tens you need after 백.

Eg: 101 → 백일   111 → 백십일   278 → 이백질십팔   663 → 륙백육십삼   880 → 팔백팔십