Iron is valuable metal, usefull for any kind of tool, but especially for weapons. It is used for knifes and swords, where it is very useful and more durable than bronze. The Bronze Age, the age when bronze was the most common material, ended around 700 BC and was followed by the Iron Age, in which iron became the most important material. The first important empire based on iron swords was the Roman Empire. But many others followed. The Middle Ages are famous for the knights and their swords. And even modern America's industrial strength rests upon a foundation of iron and its product, steel.
There are various iron ores formed during different geologic processes, and so the mining technology is rather manifold. First man tried to find very rich iron ore, which he could melt with rather low temperatures produced by wood or charcoal. Later the possibilities increased and even ore with a lower grade could be used.