The apps that are available for the iPad, can be found in the App Store, the Purchased tab. At the top left, select "iPad Apps", then choose "iPhone Apps", this will show all your purchased apps with a cloud next to them. To download them, tap the cloud.
If you purchased books from iBooks Store, open the app after installing, and go to the Purchased tab, where you will find them. Again: tap the cloud to get them to the iPad.
Hope that helps.