Tkinter - multiple windows

INTRODUCTION

'Tk' is the absolute root of the application, it is the first widget that needs to be instantiated and the GUI will shut down when it is destroyed.

'Toplevel' is a window in the application, closing the window will destroy all children widgets placed on that window, but will not shut down the program. It is possible to create many 'Toplevel' windows. They are not separate processes; if the program exits, all 'Toplevel' windows are erased.

import tkinter as tk

root = tk.Tk()   # we should start from root
root.title("root")

# Create root window contents...
# In Button, command=root.quit kills all windows.

top = tk.Toplevel()
#top = tk.Toplevel(root)   # using explicit parent
top.title("top")

# Create top window contents...
# In Button, command=top.destroy only kills the current top window.

root.mainloop()   # run the tkinter event loop
#top.mainloop()   # also works