Idk if it's helpful for you but I'll try.
ㅎ is for H
여 when romanized is written as yeo
An example of how to perceive 어 I came across was to think of it as u in up.
You need to apply the same for 여. Yu in yup. But it isn't pronounced exactly like that. Think of it as a soft yaw
So Hyu that is pronounced like Hyeo or hyaw will be written as 혀 and hyu that is pronouned exactly like hyu will be 휴.
Hope that clears it up.
ㄴ having no vowel along with it is just 'unn' like sound. Just like the n in Hyundai
대 is d+ae so dae. Like day without the y.
So it's 혀 (Hyeo) + ㄴ (n) + 대 (dae)