Design and create your material content, as you would do normally, by adding text, images, styles, …
One thing to look out for is to imagine your final page to be displayed on an iPad screen, which in general is smaller than print and asks for user hand gestures, mostly tap or slide.
This means that you might want to indicate a clickable area with either instructions or designing it in a way, that a user immediately knows where to tap, swipe, drag, etc.
Fig1: Intuitive navigation instructions
It also requires having interactive elements large enough so they can be easily tap-able with the size of a finger.
Fig2: Sizing of interactive elements
Apple recommends: Give tappable controls a hit target of about 44 x 44 points. (Minimum target size recommended by Apple for the original iOS Human Interface Guidelines).
Text should never be smaller than 11 points, even when the user chooses the extra-small text size. For comparison, the body style uses a font size of 17 points at the large size, which is the default text-size setting.
For performance reasons once the asset is exported and loaded on the iPad, it is recommended not to link Adobe Illustrator images into the InDesign file.