200x200 blue square

from tkinter import *

# Create the window
window = Tk()

# Create the canvas
canvas = Canvas(window, width=200, height=200, bg='white')

# Create the square
square = canvas.create_rectangle(0, 0, 200, 200, fill='blue')

# Pack the canvas
canvas.pack()

# Run the Tkinter event loop
window.mainloop()