How do I start production in my frontline workshop?

Once you have occupied some territories then under the territory tab in the RoC screen you will be able to use the 'harvest' button to collect the tainted resources. Then in the Honor structure tab you can tap on the production option next to the top front line workshop (if you have placed the building). This will take you to a production screen where you will have 1 (or more) queues open. Select your tainted resources to process and start.