When you create a shop, you give it a name and a shop ID. A shop name is the proper name of the shop. A shop ID is a unique and appears in the URL when someone visits your shop. Since your ShopID is part of the URL for your shop, it must be unique. No two shopkeepers can have the same ShopID.
For example, your shop name could be “My Awesome Shop”, and your shopID could be “myawesomeshop” and the URL for your customers to directly visit your shop would be https://www.cafepress.com/myawesomeshop.