from tkinter import *
root = Tk()
root.geometry('400x200')
fr = Frame(root)
bt_paint = Button(fr,width=20,text='Поява фігури')
bt_clear = Button(fr,width=20,text='Очищення полотна')
bt_paint.pack(side='left',padx=2)
bt_clear.pack(side='left',padx=2)
fr.pack(pady=5)
canv = Canvas(root,bg='white')
canv.pack(fill=BOTH,expand=1)
def clear(event):
    canv.delete(ALL)
def paint(event):
    canv.create_rectangle(180,50,50,120,fill='green')
bt_paint.bind('<Button-1>',paint)
bt_clear.bind('<Button-1>',clear)
mainloop()