To make Iron Nuggets in Minecraft, you'll need to find and mine an Iron Ore block. Depending on the version of Minecraft you're playing, you can find Iron Ore between layers 1 and 56.
Once you've mined the Iron Ore block, you'll need to put it in the furnace menu. You put the Iron Ore in the fuel box, and can receive up to nine Iron Nuggets in the result box.
Keep in mind that it will take approximately 10 seconds in the furnace to turn your Iron Ore into Iron Nuggets.
To craft with Iron Nuggets, you can use a crafting table. Put one Iron Nugget in each box of the crafting grid and you can create tools, weapons, and armor that need Iron-level durability. Items such as the Iron Pickaxe, the Iron Sword, the Iron Chestplate and more can all be crafted with Iron Nuggets.
And that's how you make Iron Nuggets in Minecraft!