[Bf-python] Blender 3D Interface

[TERRY ALSTON]

Greetings,

I am a user of Blender 3D and now I want to learn Python so that I can create plug-ins for Blender.
I've begun to search for books and Python programming tutorials on the internet, and gain some understanding of the IDE, but I'm curious about how the user interface is created. 

Is it constructed with Python, in the IDE, or is it constructed with a tool such as GTK Builder/ Glade 3.0 or Microsoft Visual Basic?

Thank you very much for any advice you can provide.

Terry