You are missing some important parts here.
You need to configure the menu first and you also need to add the cascade label.
Take a look at this code.
import tkinter
def hey():
print("hello")
def myNew():
# you forgot to use tkinter.Label here.
mlabel = tkinter.Label(root, text="yo").pack()
root = tkinter.Tk()
root.title("Wizelane")
root.geometry('400x80+350+340')
my_menu = tkinter.Menu(root)
# configure root to use my_menu widget.
root.config(menu = my_menu)
# create a menu widget to place on the menubar
file_menu = tkinter.Menu(my_menu, tearoff=0)
# add the File cascade option for drop down use
my_menu.add_cascade(label = "File", menu = file_menu)
# then add the command you want to add as a File option.
file_menu.add_command(label="New", command = myNew)
label = tkinter.Label(root, text="say hello")
label.pack()
hello = tkinter.Button(root, text="hello", command = hey)
hello.pack()
root.mainloop()
solved menubar not defined in python