Populating Photo Book captions from metadata

I want to display captions in a Photo Book using the "description" metadata. Adobe says this can be done (see following extract) but nowhere can I find out how to display captions extracted automatically from my photo's metadata.  How do you do it??

How to display captions in a Photo Book

https://www.adobepress.com/articles/article.asp?p=2999387&seqNum=3

On a single page, you can add a page caption, and a separate photo caption for each image—even if the page is based on a layout template that has no fixed text cells. Fixed text cells and photo captions can be configured for custom text or set to display captions or titles extracted automatically from your photos’ metadata.