Assuming that you are making a steam era route with wagon-load freight you will firstly, need to identify "General Goods" enabled vans to make up you consists.
Most wagon load freight was carried from railway company goods shed to goods shed or to and from private warehouses or factories. Either way, search for industry enabled assets (Tafweb has made some excellent industry enabled factories and goods sheds) or use the Auran "multi-industry basic" with an ordinary (non industry) goods shed.
The set-up otherwise is the same as for coal and oil. Trackplate, I think, has an excellent route and session based on the West Somerset Railway that includes a pick-up goods task, well worth checking out to see how it all works.
Regards
Chris