The Presentation Plugin is an extension for Grav CMS, and provides a simple way of creating fullscreen slideshows that can be navigated two-dimensionally, using the Reveal.js-library.
Installing the Presentation-skeleton can be done by downloading the newest release and extracting it to your webserver. From there it should work without issue, given that Grav's requirements are met and you've followed the installation instructions. The Admin-plugin is recommended for easy management and editing of content.
See the plugin's repository for instruction and details.