Adding a file to be "Shareable from this slide" is essentially exactly as it sounds!
With Showcase, you have the ability to dictate whether your shareable files can be shared from anywhere in your showcase (article about that here), or shareable only from specific areas within your showcase. The content you put into these lists do NOT have to already be loaded into your showcase - you are able to load files directly to these lists, without needing them in your showcase.
If you want files to be shared from a specific slide, and that slide only - here's how you go about it:
1. Open the showcase you wish to add content to. Navigate to the desired slide in which you'd like your content to be shared from.
2. Click the ‘Manage sharing’ link in the menu bar under the title of the showcase.
3. In the pop up, you will see two sections: Shareable from this slide and Shareable from all slides. To add content to Shareable from this slide - click Add File.
4. This will pull up the file picker where you can either select a file from your file library, or upload a new file.
5. Once you've uploaded your file, you're good to go! You'll see the file name loaded under the Shareable from this slide section and you can easily remove a file again by clickikng the small 'x' on the file name.
Publish your changes so they take effect! Once you've published, your file will appear in the sharing section when your users tap the sharing arrow in the right hand corner of the app:
You are also able to add content to be Shareable form this slide in the hotspot content area of the editor!
When you add content to a hotspot, or when you click on the hotspot to view what content is loaded there - you will see this checkbox below the content title.
If you check this box, the file is automatically added tot he Shareable from this slide content list. You can uncheck this at any time!