If the Forge is installed in your Hold, you can use the Forge as you smith items, and you gain benefits for doing so.
Any Skill Checks you make for the purpose of smithing gains a +5 bonus while you are using the Forge.
You smith and forge items twice as fast in the Forge, thanks to the workspaces and tools.
You have advantage on the Quality skill check that determines if the crafted items become higher quality equipment.
See: Crafting Items