Saving your web site
In WYSIWYG Web Builder you do not edit HTML pages directly. Instead a project file is being used (.wbs) which stores all pages of your website within a single file. Everytime you want to edit your website you open this project file.
To save your web site (including all pages it contains), select File->Save Web Site for the menu and enter a name for the project.
Web Builder uses the extension .wbs (Web Builder Site) to save the project files, to save your page as HTML you'll need to Publish your pages.
Publishing your web pages
Backing up your files
By default all projects file will be saved in the folder My Documents\WYSIWYG Web Builder.
So in order to backup your work, make sure you backup this whole folder, plus all folders where you have stored the websites assets (images, moves, etc).
See also this related FAQ topic:
How to copy a project from one computer to another?