How do I use the resources collected from farms on world map - rusted ignots, crooked lumber etc?

These are the items that you harvest from the resource plots in the Reign of Chaos event. You need to process them in the Frontline Workshop buildings that you build for the event around your alliance centers.

Go to the RoC menu and the Honor Structure tab to find the Production option (once you have harvested some of the resources and after you have built one or more frontline workshops).

Processing them will then give you usable resources (lumber, iron etc) and also the special materials for upgrading your honor structures in the event.