How can I create a MemberShip site?

Question

WordPress

Hello. I set myself the goal of learning how to make MemberShip sites on WordPress. To begin with, for the sake of experience, and then create a serious one for your project. To tell the truth, I do not want to use third-party plugins, firstly, in order to get the same experience, and secondly, so that I can integrate other large systems into the plugin in the future.
The problem is that I do not know the algorithm for creating at least the simplest site of this type. Therefore, I ask you, if you know what you can read, what aspects of WordPress to study or an approximate creation algorithm - write, I will be extremely grateful.
Thanks in advance!