in korean there is two counting system. the Sino Korean system(it's similar to the chinse counting) and the Native Korean system.

Sino Korean -

1 - 일 il/eel

2 - 이 i/ee

3- 삼 sam

4 - 사 sah

5 - 오 oh

6 - 육 yuk/yook or 륙 ryuk/ryook

7 - 칠 chil/cheel

8 - 팔 pal

9 - 구 gu/goo

10 - 십 shib

if you want to say 11 you would put 10 and 1 together so it would be shib-il(십일).
and 12 would be by putting 10 and 2 together so it would be shib-i(십이) and so on

20 would be i-shib(이십), 30 would be sam-shib (삼십), 40 would be sah-shib(사십)

21 would be i-shib-il (이십일), 32 would be sam-shib-i(삼십이). and so on

100 - 백 baek
and if you want to say 101 you would put together 100 and 1 so you get baek-il(백일)
and if you wan to say 110 you would say baek-shib(백십)
and 111 would be baek-shib-il (백십일)
200 would be i-baek(이백), 300 would be sam-baek (삼백) and so on

1000 - 천 cheon/chun.
1001 would be cheon-il(천일)
1011 would be cheon-shib-il (천십일)
1111 would be cheon-baek-shib-il (천십백일)
2000 would be i-cheon(이천), 2001 would be i-cheon-il(이천일) and so on

get it? you have to ad a number in the start or in the end.

10,000 - 만 man
100,000 - 십만 shib-man
1,000,000 - 백만 baek-man
10,000,000 - 천만 cheon-man

100,000,000 - 억 eok
1,000,000,000 - 십억 shib-eok
10,000,000,000 - 백억 baek-eok
100,000,000,000 - 천억 cheon-eok

1,000,000,000,000 - 조 jo