To answer your question, download the epub file to your computer, then drag and drop directly to iTunes. ITunes will automatically add it to there book section. If you haven't downloaded iBooks app, go ahead and download it to your iPad. Finally sync your iPad with your computer and iTunes will drop your epub books into your iPad for you. Disconnect and open up your iBooks app and there they are, ready for reading. One of my favorite web sites for books is
www.feedbooks.com
Enjoy your reading!