This dialog appears when you right-click a navigation item and select Button Type > Image Button from the shortcut menu. It helps you to specify the source of the image button. See the dialog.
URL
Specify the source of the image button from a URL. You can click the Browse button to specify the path or input the URL directly in the text field.
OK
Applies the changes and closes the dialog.
Cancel
Does not retain any changes and closes the dialog.
Help
Displays this help document.