You are in the General Properties tab of a module template. For more information, see Configuring General Properties for a Module Template.
To use a URL to provide the icon, you have completed the steps described in Enabling the Use of Images from URLs.
You can select an icon from the image gallery, or upload an icon from the file system or from a URL. Every icon you upload is added to the image gallery. For information on deleting icons, see Managing Module Templates.