Proto-websites - technically called hypermedia, it was basically a locally stored website, and pioneers were trying things out like putting books and information and functionality in them. In this case, it's the Wintermute trilogy by William Gibson in Hypercard format, so this is also a retro computing discovery.

"The Expanded Books Project was a project by The Voyager Company during 1991, that investigated how a book could be presented on a computer screen in a way that would be both familiar and useful to regular book readers. The project focused on perfecting font choice, font size, line spacing, margin notes, book marks, and other publishing details to work in digital format."

What exactly are you unclear on?

Edit: not sure why I was downvoted, I’m literally attempting to provide whatever information you need about this, just not sure what aspect is confusing.