To combine multiple tkinter windows, you can create a new window by instantiating a new Tk() object, and then place widgets on it using the pack(), grid(), or place() methods. You can also add buttons that when clicked, open another window using the Toplevel() class. This allows you to create a hierarchy of windows, with the main window acting as the parent and additional windows as children. By organizing your windows in this way, you can create a more complex and user-friendly GUI application.