How do I apply a Blend4Web module similar to the plane flight preview? I am trying to make a load screen to fit my scene.

This has a custom load screen to fit the scene:
https://www.blend4web.com/en/demo/island/

This is the API:
https://www.blend4web.com/api_doc/module-preloader.html

But I can't find how to apply or use the API. How do I apply a Blend4Web module?
Please take a look at the source files of the Island demo you mentioned.

https://github.com/TriumphLLC/Blend4Web/tree/master/apps_dev/flight

Search for create_advanced_preloader in the flight.js file.