In the link you provided it explains what you must do.
The Consume credits icon means the layer consumes credits. Check the Use proxy check box to allow public users access to a layer through your subscription. Optionally, set Request Limit and Interval to control the usage.
Sorry I posted the wrong portion.
If you want to share your secure service item with the public, for example, as part of a public web app, store the credentials with the item so the public is not required to log in to access your app. See ArcGIS Server web services for more information.