from tkinter import *

root = Tk()
root.geometry("400x300")

def abrir_form():
    # top level
    top = Toplevel()
    top.title("Novo Formulário")
    top.geometry("200x100")
    lb1 = Label(top, text="Label na nova janela")
    lb1.pack()

cmd = Button(root, text="New Form", command=abrir_form)
cmd.pack()

root.mainloop()
from tkinter import *

root = Tk()
root.geometry("400x300")

def abrir_form():
    # top level
    top = Toplevel()
    top.title("Novo Formulário")
    top.geometry("200x100")
    lb1 = Label(top, text="Label na nova janela")
    lb1.pack()

cmd = Button(root, text="New Form", command=abrir_form)
cmd.pack()

root.mainloop()
# top level