Merchant Account for eBay with CSI comes with Shopping Cart?

I just set up a merchant account with CSI (Card Services International). They come with a free shopping cart for eBay. I sell only on eBay. My question is do I also need a Gateway as well to be able to integrate my merchant account with the shopping cart on eBay or does the free shopping cart on eBay give me a Gateway already. I'm very confused!