First watch some tutorials. They're free and will give you an idea of what you need.http://www.chefknivestogo.com/knshforne1.html
There is only 1 item you need to purchase to get started. A stone.
This combo stone is a good one to start with:http://www.chefknivestogo.com/imtwosi1kst.html
If you use this stone a few times, enjoy sharpening and want to keep adding accessories the next thing I would buy is a good flattener like this one:http://www.chefknivestogo.com/dmtextracoarse.html
I holder comes in handy and that would be the next thing I would get. I love sharpening on my sink bridge in my kitchen.http://www.chefknivestogo.com/nasibr.html
There are other items you could add to this but this would be plenty to start.