How to make equipment for a mob.

During the creation of my mod, I came to a dead end. How can I create equipment for a mob, and how can I make it possible for a mob to wear this equipment? I also want to figure out how to make the equipment displayed on the mob. An example of equipment is armor and a chest that allows the mob to carry things. I also use the geckolib plugin. 

This was implemented in the Mythic Mounts mod, which also uses the geckolib plugin.(for reference)

 I apologize for possible grammatical errors, English is not my native language.