Hello and welcome,
You can find current books for sale at www.fictionwise.com
, scroll down and click the Gemstar/Rocket eBook link under formats. This is a good way to get content without needing to convert it but I'm way too cheap to pay for my books so I read public domain stuff and most if not all requires conversion.
The Baen Free Library
has SciFi books in .RB format. You can download ISO's of quite a few (30 at this writing) Baen cds here
give links to different versions of the librarian software.
The USB cable is standard but it would be a good idea to take the ebook with you to try out cables.
gives you info on the charger.