Fundamentally, an eCommerce experience is about getting order information from the customer and passing it to the manufacturing, fulfillment, and finance functions.  Additionally, it’s often desired to bring information the other way (for example, to allow a customer to view and pay past invoices online).  In both cases, this typically requires an integration between the ecommerce platform (that the customer interacts with) and the ERP, which houses the data and serves the other, internal functions.  This integration can be as simple as exporting/importing spreadsheets by hand or as sophisticated as a real-time connection between the systems, providing instant access to live data.