When you count any nouns, you attach counting units in Korean.
For example, if you count people, you will use a counting unit for people.
Korean number system with counting units
Something you need to remember is you generally use Korean number system.
And, from 1 to 4 and 20 get shorten, when you use number with counting units.
하나 becomes 한,
둘 becomes 두,
셋 becomes 세,
넷 becomes 네
스물 becomes 스무.
Any numbers that end with other numbers(5-9) don't change,
meaning 11-14 will change, but not 15-19.
I believe it is easier to pronounce them with counting units, when they are shorten.
When used with counting units
How to add counting units
The position of counting units is 'noun + number + counting unit'.
Like the example of the left video above, when you count flowers,
you say 'flower 꽃 + number + counting unit 송이'. 꽃 can be omittied.
In this case of the right video above, it will be 'people 사람 + number + counting unit 명 / 분'.
명 is casual and 분 is a polite counting unit.
For example of 3 people, you will say '사람 세 명'.
Now, we learned where counting unts are positioned.
It's time to learn the variety of counting units.!
There are many of them and actually many more than the table below.
Please feel free to do your own research as well. :)
general nouns that don't have specific counting units.