How do I add captions to my book?

On iOS:
To add a caption to a photo in your book, simply tap on the page to open 'Page View'. Next, tap 'Caption' at the bottom of the screen, type in the caption you would like, and then tap the blue 'Done' button. If you have more captions to enter, tap the arrows on the left or right side of the screen to switch to other pages. When you are finished, tap 'Book View' at the top of the screen to save your changes.

On Android:
To add a caption to a photo in your book, simply tap on the page. Next, tap 'Caption' at the bottom of the screen, tap the text box, and then begin typing in the caption you would like. Once finished, tap the checkmark at the bottom of the screen. If you have more captions to enter, tap the arrows on the left or right side of the screen to switch to other pages. When you are finished with all of your captions, tap 'Done' at the top of the screen to save your changes.