The adminstartion for the shopping cart is found at http://www.yourdomain.com/shop/owner/ (where 'yourdomain.com' is replaced with your actual domain name). The Shop Owner's control panel is a simple, web-based interface where you can add items and configure your shop.
(click here for larger image)
When you go to the shop control panel, you will come to a Login Page that looks like the image provided. You will need to enter the password in the box marked 'Password'. Your password will be listed in your 'Web Site Settings Email' sent to you when you created your account.
You will also see the 'User Login' button to the upper right. If you have multiple users set up in the shop, you can use this function. If not, you will not have to worry about it.