How do I download books to my Ipad

You can use the iBooks application, or something like the Kindle app.

Depends on where you buy the book. There is a Kindle app, and a B&N Nook app, and of course, Apple's iBook app. However, if you buy books from an online seller in DRM ePub format that requires Abode Digital Editions to authorize it and move it onto a device, you will be out of luck (at least for the time being).

and if it's non DRM books in epub or pdf you can just add them to books in itunes and sync with the ipad