

It is not necessary to unlock the recipes, but some of them require a certain level of crafting / blacksmithing. When you move them together again, the game asks you whether you want to craft or just combine them. If the recipes require 2 of the same item (Large Steel Bar = 2 Steel Bars) you can split the pile in your inventory using the Shift key.

To craft something just drag the items over each other in the inventory.
