You can upload a slide deck into the Glisser platform in either PowerPoint format (PPT or PPTX) or PDF. So if you are creating your presentation outside of PowerPoint (i.e. Apple Keynote, Google Slides etc.) then you’ll have to save/export your file out as a PDF file to upload.
If you’ve created your presentation in Prezi, see here for details on how to use it in Glisser.