In English, numbers are divided into 3digits(I’m not sure how to descrive this, I hope you get the right meaning)
you need to know
100 hundred
1,000 thousand
10,000 ten thousands
100,000 one hundred thousands
1,000000 million
In Korean, numbers are divided into 4 digits when we read them.
(But they write it with 3-digit division, usually at the banks)
1 일
10 (일)십
100 (일)백
1000 (일)천
10000 (일)만
then, repeats in the cycle
100000 십만
1000000 백만
10000000 천만
100000000 (일)억
1000000000 십억
10000000000 백억
100000000000 천억
100000000000 (일)조
예) 123456789 일억 이천 삼백 사십 오만 육천 칠백 팔십 구
So, you need to know 십, 백, 천, 만, then, 억, 조,…bigger numbers than this will not be heard often around.