How do you come up with your own cookie recipes?

Hi, i love to bake, and i can bake really well. I would love to start my own baking cakes/cookie business, but i cant use the recipes i’ve been using right?
How do you come up with making your own recipes? like proportions, and know exactly what recipe needs what in it?
do i need to go to school for that? or is there a system to find this out?