By default, when you create a Web Page it will assign the Image as Spinner and will assign the text as "Loading …" for each partition language. Both of these values can be customized.
But what does it do? When attempt to load a page and there are delays loading the content you will be presented with something like this.
To customize the spinner, change it via the settings in the Integration tab:
Tip – The image associated with the Loading Screen will only be shown if your Web Page takes longer than a second to load and it disappears again when your RDMLX starts to execute. If you don't see the image try slowing your browser down.
In Chrome, select the Developer Tools (F12) and the modify the Network settings to disable caching and slow the network to something like 3G speed. Now reload your Web Page.