PowerPoint comes with a number of design templates that are always available from the Slide Design task pane. Each template has unique font and bullet styles; a background design; a color scheme; a layout—all the basic style elements for a slide.
But part of the fun of PowerPoint is being able to tinker, and a typical example of this is customizing an existing template (such as the basic blank design) with your own fonts, colors, and background. Once you've customized a design template, you're likely to want to use it in other presentations. Browse helps you do that.