main lop in python tkinter

[barryjo]

I am trying to do what the above code does, I think. I have a hard time following the code. Here is what I want..
In the snippit below, I would like to see "test" printed out every 10 milliseconds.
I don't think I am using the after properly. What should I do?

def PrintIt()
   print ("test")

root = tk.Tk()
button1 = tk.button(bla bla......

root.after(10, PrintIt)
root.mainloop()