Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
Since you entered the Web module, you’ve been working with an unsaved web gallery, as is indicated in the bar across the top of the Slideshow Editor view.
Until you save your gallery design, the Web module works like a scratch pad. You can move to another module, or even close Lightroom, and find your settings unchanged when you return, but if you click a new gallery template—or even the one you started with—in the Template Browser, the “scratch pad” will be cleared and all your work will be lost.
Converting your project to a Saved Slideshow not only preserves your layout and output settings, but also links your layout to the particular set of images for which it was designed.