Smelting

If you tried to create iron tools with the blocks of iron that you have mined, you noticed that you can't create iron tools. The reason why is that you need to create iron bars, which is done by smelting.

You need to place the iron ore in the top slot of the furnace interface and something that burns in the bottom slot of the furnace. Wood, planks, wooden tools, saplings, coal, charcoal, lava and many other items can be burnt in the bottom of the furnace. Try not to smelt all of your ore if you can if you have more than 5 ores, just smelt 5.

Now that you have 5 iron bars you should craft an iron furnace, this will increase the length of an item that burns in the furnace and increase the speed of which something smelts so this will save you time and resources. This is the basics of the smelting, but there will be other furnaces later into the game and those will be covered also.