Each map has one factory that can be purchased for a large price. The factory will produce any items, weapons or vehicles that you have Blueprints for.
Buying the Factory
Head to the factory icon on the map and use the "Y" menu to purchase. If it isnt showing up, move further away from any other nearby buildings. The Factory and Businesses are purchased using Resistance Funds and must be purchased by a General.
Operating the Factory
Once owned, any general can go to the location and use the "Y" menu > Manage to add items to the queue. Clicking on an item to the left will show the required funds and resources to the right.
Steel, Wood and Plastic required for production need to be put in the large green container that spawns near the factory icon. If the container is removed or destroyed just wait and another will spawn.
Main Article: Blueprints
Blueprints can be purchased from various faction dealers (represented by a flag icon on a house) or reverse-engineered from existing items (in your inventory or nearby vehicles) via the "Reverse-Engineer" button in the factory manage screen.
Items and vehicles can be queued and the factory will consume resources at the start of production. If you remove that item from the queue before it's finished those resources will be lost. When completed, any vehicles will spawn nearby and weapons/items will appear in the large green container where the resources go.