When to use "ㅇ"?
Sorry, the last time I typed this I accidentally put it as a notebook entry.
But when I see "ㅇ" it is used in two ways like in "안녕하세요" it is used as both a place holder and also to make the sound "ng"

Question

Answer

Vowels can't stand alone. So you have to put ㅇ for it. - the Placeholder.  For example 안녕하세요 | the ㅏ can't stand alone so you have to put the ㅇ for the ㅏ= 아. You don't have to do it when there is a consonant for the vowel for example 만나 ~ hope it helps