Actualy, there is no a big secret about that letter. English native speakers pronounce the same sound everytime in english. The "r" sound is the same "r" sound you can hear in words like "rock", "river","rabit", etc. And the "l" also sounds the same in English and Korean. When the letter ㄹ is located as a first letter of a silable, it sounds as "r", and when it is located at the end of a silable it sounds as "l". For example: 라면 : ramyeon , 살다 : Salda Also, when asilable ends with ㄹ and there is a following silable which starts with a vowel such as 아, 애, 에, 어, 오,우,으,요,유,etc, the sound of ㄹ changes from "l' to "r". P.S: If I may, I would like to give you an advice. Don't focus all your attention to that letter or unconciously it is going to become mroe and more difficult to you.
As I previously explained it to you, there is no a big deal about that letter and I am sure that you will be able to understand it well and leave behind your confusion about it.
I hope I had helped you !
Cristian