import tkinter
import tkinter.messagebox

def click_btn():
    tkinter.messagebox.showinfo('資訊', '點選按鈕了')

root = tkinter.Tk()
root.title('第一個訊息方塊')
root.geometry('400x200')
btn = tkinter.Button(text = '測試', command = click_btn)
btn.pack()
root.mainloop()