You can't shop directly from your Kindle for iPad app, due to Apple restrictions. You can purchase content from the Kindle Store on the Amazon website, using your Safari web browser.
To quickly access the Kindle Store from your Apple device:
Hello Forum people, My name is Zach and I am a Moderator for Amazon. I enjoy Film Making, Graphic Design and Web Design in my free time (Different than Kindle Freetime of course). I am also an avid adventurer, looking forward to my next outing!