Shop source refers to product sources, which you have decided to publish on your shops at virtual marketplaces or e-commerce sites.
You dont have to use every product source that you have identified to the system in every shop of yours. You can choose in which shops you are going to use your product sources on shop sources section. For example if you have identified 4 xml then you have 4product source. Assume that you have 2 shops, while you are using one of your product source in one shop, you can use the other four sources on the other shop. Also, you can make advertisement template settings separately for 2 shops’ xml that you use together and make the sales with different commisions.