Adding books to the iPad, iPhone or iTouch (hereinafter collectively referred to as iThing) is done via a process called sideloading. You must use iTunes.
Step 1. Connect your iThing to the computer using the USB cord.
Step 2. Open iTunes. iTunes may open automatically when you connect your device depending on your settings.
Step 3: Using iBooks. On the upper left hand side of iTunes is the Music, Movies, TV Shows, etc. list. There is also a Books link. Click on that and a window for your books will show up.
You can add books by dragging and dropping onto this window or use the File -> Add to Library command. Skip to step 7.
Step 4: For all apps other than iBooks, once iTunes is open, navigate to Apps tab.
Step 5: Scroll to the bottom under sync apps and the screenshots of your iThing to where it says “File Sharing”. On the left will be a list of Apps that allow you to add books and other files and on the right is a blank area where you will drag and drop your ePub files.
As you can see here, I have Kobo, Stanza, Bluefire, and Borders. Only Bluefire will accept books that have a software lock called DRM. The rest of the apps will accept non DRM’ed epubs only. Kindle and nook apps do not read sideloaded books.
Step 6: Select the app that you want to use to read your ePub by clicking your mouse on it. It should be highlighted. Then drag and drop the epubs you want to read onto the area on the right.
It may be easier to drag and drop if you resize your iTunes window:
Step 7: Sync your device.
Step 8: Eject and read!