To load the Kindle file (.mobi) on any Kindle device or in any Kindle app, first upload it to the Kindle Personal Documents Service. This service will allow the file to be treated like any Kindle book you purchase from Amazon, including syncing your bookmarks, reading location, highlights, etc. between your devices.
To load the EPUB file in iBooks on an iPad/iPhone, etc., add it to your iTunes library choosing File > Add to Library, or drag the EPUB file to the Books library in iTunes on your computer. Then just sync your device with iTunes to add the book to your iBooks library. Alternatively, you can visit the book download page on our website in your iPad browser (Safari, etc.) and click on the download link. That will open up a dialog on your device asking if you want to load the file in iBooks.
Here is a helpful video about how to sideload the EPUB file on a NOOK device.
To load the EPUB file on a Kobo device, use the Kobo Desktop application.