[1.15.2] Custom drop from entities? (GlobalLootModifier)

[discodancer]

GlobalLootModifier  <-  I've been trying to understand what this thing is for about 4 days with no result!!!

 

What should I do (which classes, jsons, folders should I create),(example codes best) to add new items to drop from entities (for example: wither_skeleton now drops 1-2 diamonds on death).

- If you know the mods which use GLM show me them pls.

- If you have an UNDERSTANDABLE instruction (not like millions of unexplained strings of code)

- If you know a video which is about GLM pls give me the link.

As you can understand I am not that one who is 5 years in Java and modding already so imagine as if you were talking to a baby.

 

P.S. If I was not clear up yonder I can illustrate what my need is.