If you did, then you might not have heard of a great piece of software called Calibre.
This not only allows you to manage your ebooks that you download or buy, you can send them to your reader, either directly connected to your PC or you can email them to your kindle application.
I use it extensively , and I'm more than happy to answer any questions you may have using it - though it is very easy once you get started and follow the install wizard.
It works with Linux, Apple OSX and Windows 7 (not sure about 8).
Give it a go, you will find it very handy I'm sure.
Also, if anyone has any really good free ebook sites they would like to share, then we can keep them in this thread.
Regards
Nick