The Source Interface tab appears when you choose to ship against a source interface document (such as an order). The fields will vary depending upon your source interface.
if your source interface uses Batch IDs, this tab would include Batch ID selection for the current shipment.
If your source interface supports freight and notes write-back, the shipment's Write-Back status would appear.
if your source interface supports Shipper IDs, the Shipper IDs associated with the currently connected Company would populate a drop-down list.