The Fun-Sized Forge one of the means in getting new equipment, as you can find recipes across Erdrea in order to create those items. Recipes can be found via red books on bookshelves, in chests, and even as rewards from quests. In the original version of the game, you can only access the Forge at campsites, while you have access to it anywhere in the Definitive Edition. Each item you attempt to craft will require materials, with the Definitive Edition allowing you to purchase some materials straight from the forging screen. To get this, you need to forge any ten items, so once you get enough recipes, craft the ten different items to get the trophy/achievement. It doesn’t seem like it matters if you fail or not, as the item is still crafted in the end.