You do not download it, its a free site which you list on then your ad is posted to ebay. They are much more user friendly.
What I love about it is you can pre set your profiles, so I have a profile set for different weights and whenever I list anything I just pop it on the scales and select the correct profile, so you can pre-set all your postage costs for at home and abroad.
If you have a look at their site they have tutorials which are worth a look at, it took me a while to get my head around it but when you are up and running you will never look back.