How do custom sounds work in the newest update

How do custom sounds work in the newest updaate. I would like to know how to set them up so I can use custom sounds

 

How about waiting until theyactually implement a better sound system first. The current in 0420 is experimental, plus it only works on the Covet. What would be the point? It's like a proof-of-concept sort of thing...

 

I have seen mods that have custom sounds. Such as this mod updated-for-0-4-2-0-Strato-HMX-920-Aerobatic-Aircraft. So how would you use custom sounds in a mod.