In addition to reading ebooks online, you can download them to read on your device. The advantage of downloading is that you don't need Internet access, once you've downloaded and opened the ebook. The disadvantage of downloading is that it is a little more complicated. 

To be able to read downloaded books, you need to install Adobe Digital Editions. This is like Adobe Reader, but it necessary to read Digital Rights Management (DRM)-controlled files. This tutorial goes through the installation of Adobe Digital Editions step-by-step

The download page for Adobe Digital Editions has links to versions for:

Once you have Adobe Digital Editions installed, you can download ebooks. It's a straightforward process but does require some clicking. When you click on the download button, a box will display

Select your device type and whether it's your own, or a public device and click Continue

If you have not installed Adobe Digital Editions, you will need to click on Get Adobe Digital Editions

If you have installed Adobe Digital Editions, click on Done with this step

Select the number of days for which you want to keep the book (1,7,14 or 21) and click the download button. Some books may be available as pdf and or epub. Choose the format you want.

After clicking the download button, a download box will open

You should choose to open the file rather than save it. If you choose to save the file, you'll need an Internet connection to be able to open the book later, but if you open the book now, you won't need an Internet connection later (it's to do with DRM)..