You can craft Iron Bundles using the construction Skill at a Construction Bench (assuming you have one). If you don't have one, then you need to buy one from the general merchant, she sells work benches occasionally. Crafting benches can also rarely drop from chests.
You can craft ingots, both Iron and Copper in the Forge, you don't need an actual Skill for that. You do need the Skill if you plan to use any of the work benches though.
You can also buy the Ingots from the Goblin Smith as Musical74 has mentioned.