Thank you so much!You really helped me a lot

It is a place holder. Quoted from https://www.reddit.com/r/Korean/comments/ababo/beginner_%E3%85%87_the_placeholder/ So by now you've seen the consonant 'ㅇ' used alot, especially with verb conjugation. It's important to emphasize the sound this consonant makes. We know that each syllable must have atleast one consonant and one vowel, but what happens when we want to make an 'ah' sound? We only need a vowel to make that sound but to make a syllable we need a consonant. That's where 'ㅇ' comes in. * When placed first in the syllable 'ㅇ' has no sound.* Thus, 아 sounds like 'ah' as if only ㅏ is there. What about when we place 'ㅇ' at the end of a syllable? I mean, it is a consonant. So for example the first syllable of the word 행복 which means happiness, 행. When placed at the end of a syllable, 'ㅇ', sounds like 'ng'. So ㅎ + ㅐ + ㅇ = h + ae + ng = haeng. Pretty simple if it's at the beginning it's silent and at the end has an 'ng' sound.