Just FYI, you've posted in the wrong place, this part of the discussions site is for iBook Author, you should post in iBooks.
Anyway, if you're on your mobile device, you open IBooks (you may have to download the app from the AppStore, I don't think it's there by default), tap 'store', and search for 'Jeremy Clarkson'. Latest book I could see is "the Top Gear Years".
If you're on your mac, the iBook store can be accessed via iTunes, downloaded, and then sync your iPad.
Hope that helps.