You've created your new library, called Popular Slides. Now you can publish slides to it.
To do that, you click Upload and click Publish Slides. This will open PowerPoint 2007 and a browse window that enables you to look for the presentation with the slides you want to publish. You can publish all of a presentation's slides, or just a selection of them. Click Play to see an animation showing this process.
Note You can publish slides created in PowerPoint 2007 or earlier file formats. Slides in earlier file formats are converted to the PowerPoint 2007 format (.pptx).