The Forge is the second crafting station you can use in Valheim. You can build it after you have access to Stone, Coal, Wood, and Copper. Once you have those four, the crafting recipe will unlock and it is craftable via the Hammer. Also, take note that to build it you need to be in the vicinity of a Workbench!
The forge works similarly to the Workbench, but focuses more on metals:
The forge is responsible for crafting metal-based weapons, armors, and tools in the game!
You can upgrade metal tools and armor by selecting the Upgrade tab in the right menu when interacting with the forge. This increases the items stats per upgrade for a small resource cost.
You can repair your gear by interacting with the forge then pressing the glowing hammer icon on the lefthand side of the right menu. This costs nothing and will fully replenish your item’s durability.
You can upgrade the forge level by placing certain objects in its vicinity. It allows you to build even more items. Each item in its vicinity will increase the forge level by one, and you can tell if an item affects the forge by checking if glowing lights appear linking it to the forge when your reticule is on it.
You can craft Anvils once you have acquired Bronze.
You can craft Forge Coolers once you get Copper and Fine Wood. Chop down Birch Trees (white-trunk trees) to get Fine Wood!
More upgrade methods will be added soon!