Final answer:
To close an application window on an iMac interface, you should click the red button at the upper left corner of the window.
Step-by-step explanation:
To close an application window on an iMac interface, you should click the red button at the upper left corner of the window. The red button is commonly known as the close button and is used to exit or close the application. Clicking this button will shut down the specific application window while keeping other open windows intact.