How to use sound sources?

I know I make a lot of posts askign for help sorry I don't mean to burden anyone I'm just trying to get a better understanding on how to create mobs and I've learned a lot this week

So I need to find out how to add sound sources for instance

entity.ghast.ambient #This is the main sound

mob/ghast/moan1
mob/ghast/moan2
mob/ghast/moan3
mob/ghast/moan4 #These are the sounds it chooses from
mob/ghast/moan5
mob/ghast/moan6
mob/ghast/moan7

How can I setup one of those moans as a sound...

How to use sound sources?