How gui libraries work ?

Question

I learned about pygame and kivy in python lang. , and I m wondering on how this libraries can change the color of pixels, drawing on screen .when I can t write something like that with only built-in function !!

Answer 1

tkinter is built-in and you can do stuff with it.

Answer 2

maybe the app tells OS to draw something, then the OS, which has full control of hardware including monitor, actually draws things?