"Generate HTML File" reads an HTML file and create new one.
If there are css, js, png, gif, jpg files in this file, the contents of these files are read and inserted into the new HTML file. Line breaks are removed to.
This node does nothing in shipping build. You do not need to remove it in shipping build.

"Load HTML File" loads the newly created HTML file into the browser.

Recommended directory structure:

D:\myUnrealProject\Content\HTML\dev\myHtmlFile.html
This is the development directory for the HTML page. It does not have to be located in the Unreal project. It can be located anywhere on the system.

Content\HTML\run
This is the directory in the project that contains the HTML files Unreal is supposed to use. These files are generated by the “Generate HTML File” node. This directory should be included in the .pak file.