Ok, the first thing you probably need to do is log into Adobe and create an adobe account. Here is the link:https://www.adobe.com/cfusion/membership/index.cfm?nf=1&nl=1&loc=en_us
Next, in Overdrive click the menu then the Apps Settings button at the bottom. Page down and type in your Adobe ID (email address) and password then click authorize. I am not sure why Adobe makes you do this. It seems like a silly extra step.
Next click menu and select Get Books. Here is where you will add a library website from which you will download your books. Here is a link that let's you search for bookstores and libraries that use Overdrive for distribution. There seems to be about 12 bookstores in the States to download books including Barnes and Noble and Borders.http://search.overdrive.com/
Once you add a website, you click on it and work through that website's download process.
For my library, I can search for a book, "check it out" and download it right from my Archos. After that I just open it up from the main menu in Overdrive.
It's actually a pretty good reader.