Quoted from
https://hinative.com/en-US/questions/3560112
When the noun start with ㄹ, sounds as L and when it is middle it depends.
ex : 라디오 ladio(radio), 리듬 lideum(rythm), 라면 lamyun(ramen)
When in the middle, consider r sounds as Spanish not like american not wr~
ex :도레미 doremi, 가르치다 garchida(teach), 고래 gorae(whale)
As you can see, when ㄹ is after symbol without 받침(batchim, which means final consonant), then it sounds like R. But when ㄹ is after symbol with 받침, it sounds like, L 한랭hanlaeng(cold), 말리다 malida(dry), 몰라요molayo(I don't know).
Actually, Koreans do not have r sound. Also, the quality of L sound is slightly different from ㄹ sound. But L is more similar than r. Because we always touch the alveolar ridge (The ridge right behind the upper teeth) when pronouncing ㄹ.
(You know that the tongue tip doesn't touch there when pronouncing R.)
ㅇ has two different sounds.
As a first consonant, it has no sound. it is a place holder.
ex: 아a, 우u, 요yo
As a final consonant, it has /ng/ sound.
ex: 강gang, 동dong