Process for turning mesh into character morph?

Sorry for the broad question, I am very new to this. Pointing me toward any resources for me to learn would be helpful. Right now, I have this character “morph” that is basically just a mesh that the character wears as a hat, but this hat covers the character’s entire body. This results in a very robotic look with no limb movement. What does the big picture process look like for taking this mesh and dividing it up into the R15 character parts and then applying those parts to the player? Also, can humanoid descriptions be used with custom character parts?