Mesh based constuction/addon/build system

I want to pretty much do a build system similar Anyland’s; in which I can take a mesh and addon/modify it at will.
Are there any tutorials or information on how Anyland did their system?
I some-what understand some of the background logic and how most of the variables/parameters to the meshs are exposed and dynamic to the user input and maybe some interfaces are used.
I don’t get how to add other meshs to the one I am already touching or how the interfaces work in that regard if used?