How to create a new Enigma2 flavor?

Hello. Can somebody please explain to me the steps for creating a new Enigma2 flavor? I would like to try and create my own custom OS, but I do not know how or where to begin? All of the instructions that I found so far explain how to compile existing Enigma2 flavors. How do I get the core of the system, compile it, and add my own features? How do I flash a set-top-box and install the custom OS onto it? Thank you