Minecraft wiki entry for The_second_day, associated text: Iron is probably the most important and versatile resource you can find underground, and it seems there is never enough of it. You can use it to craft good quality tools, armor, and a variety of other things. For your second day (or whenever you venture underground), your initial goal is to get at least 33 pieces of iron ore (see below for what to craft with that), and more iron is always needed and useful. Once you have some of the ore, use a furnace to smelt it into iron ingots, that you can then craft into other items. Remember that to mine the ore, a stone pickaxe is required.