When running code, it opens two windows and I cannot understand why [closed]

tk.Tk() creates first window, and tk.Toplevel() creates second window.

You need only tk.Tk() to create Account window (main window in program).

For Main window you may need only tk.Toplevel() without mainloop() - if it has to be subwindow (and still display Account window).
If you want to replace Account window then Main will need only tk.Tk() with mainloop().

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After running code I see also problem with

account.destroy() account.iconify() account.deiconify()

if you destroyed window account then you can't run iconify and deiconify because window doesn't exist - and this raise error.

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Full working code with some comments in code.

Because I didn't have any image so I skiped part with PhotoImage

import tkinter as tk def Main(): main = tk.Tk() main.title("Hello Budgeting software!") entry = tk.Entry(main, font=("Comic Sans", 30), fg="#00ff00", bg="#000000") entry.pack(side="left") main.mainloop() def Account(): global user global password account = tk.Tk() # it creates main window (if you assign another window to `account` then this window will be empty) def clear(event): if event.num == 1: # left mouse button user.delete(0, tk.END) else: user.delete(0, tk.END) def spark(event): if event.num == 1: # left mouse button password.delete(0, tk.END) password.config(show="*") else: password.delete(0, tk.END) password.config(show="*") def submit(): account.destroy() # account.iconify() # account.deiconify() Main() # account = tk.Toplevel() # it creates another window (subwindow) account.geometry("650x650") account.title("Hello Bank Account!") label = tk.Label( account, text=("Hello Bank Account!"), font=("Arial", 18), relief="raised", bd=10, padx=20, pady=20, ) label.place(x=190, y=10) user = tk.Entry(account, font=("Arial", 18), relief="raised", bd=5) user.insert(0, "Enter User") user.bind("<Button-1>", clear) user.place(x=190, y=150) password = tk.Entry(account, font=("Arial", 18), relief="raised", bd=5) password.insert(0, "Enter Password") password.bind("<Button-1>", spark) password.place(x=190, y=200) # icon = tk.PhotoImage(file="arrow.png") # account.iconphoto(True, icon) submit_button = tk.Button(account, text="OK", command=submit) # image=icon, submit_button.pack(side="right") account.mainloop() Account()