In the town of Gorhart inside The Corner Shop you will find a Blacksmith forge. Simply walk up to it and activate it. Then select Craft from the menu. You need to have enough crafting materials to create the items.
For me personally (playing a rogue build) I did not put any points in Blacksmithing yet but was still able to make a few pieces of armor. I looted a Greaves Core and a Lining off of some dead bodies / chests found in the world and was able to construct a pair of Greaves pretty early on in the story. After you create your first item, the trophy will unlock.
If you're struggling for components, there are a few Blacksmith supplies in the chest to the left of the forge. It is not a crime to loot from this chest. Otherwise spend some time searching the areas just outside of town (especially the overturned carts near the bandit areas to the North) for components.