There are 2 options to download the book to your iPad.

1. Visit Log in to the site. On the download page, click on the link to download the book. It will open on your ipad. To save it to your Ipad for offline reading, tap near the top right corner. "Open in Itunes" and "Open in..." will appear in the corner. Click on either. I would choose "Open in..." and the Kindle app, but I prefer Kindle to iBooks.

2. On your computer, download the file. In Itunes, click on File. Then Add to Library to add the file to your library. Then you can connect your iPad and sync the file that way.