You should be able to plug it in to your USB port and is the Gods are smiling on you, the memory and/or memory cards in the reader will show up as drives on your computer. You can drag and drop epub books there and they should show up on the 505 after you disconnect (and allow it to think about it a bit)
You'll probably want to install the Sony Library software (should be on a CD, but the online site may have updated software -
http://ebookstore.sony.com/ it has a download link in the upper right.
With it you can purchase books from the Sony store.
Hope that is helpful.
Ask if you have further questions.
You may want to look at Calibre for managing your library as well.