To create a slideshow, you just need to download the submissions from the Game Manager (where you created the game). To do so, head to the "Submissions" tab for your game and click the "Download Submissions" button in the top right.
From there, select how you want to zip the submissions together (e.g. sorted by team or by mission), wait for the zip file to be created, and then download that zip file. From there, you can unzip the zip file from your computer and create a slideshow however you’d like!