The Autofill feature is a perfect way to add multiple photos to your slideshow.
Choose a template from our catalog and click Customize to enter the editor:
Add photos to the photo library by clicking Add photos:
Then click on Auto-fill on the right toolbar on the editor:
Your photos will appear on your slideshow. You can then re-order them if you choose to (How to Rearrange Your Slides).
Note: You must have a minimum of 10 photos and a maximum of 50 photos in the photo well at one time, for the Auto-fill feature to work.