You can find this section in HostBill Admin → Settings → Products & Services → Your order page → Your product → Connect with App

Once you add your new product, this tab gives possibility to connect your product with the Third party apps. From the dropdown menu you can choose a module which will be used by the product after the order is placed. Note: The list displays only activated modules - Activate the module first and connect it with HostBill. 

Depending on the module, you will be presented with various configuration options.

To learn more about specific modules visit Configure Provisioning Modules articles.