As you might already know, people used tools made of stone in so-called Stone Age. Prehistoric people used to dig and mine for useful stones and minerals, like flint.
Perhaps one day, a prehistoric miner found what is now called native copper. It's distinct metallic look means it was great for making jewelry and ceremonial tools. The prehistoric people probably tried to alter the shape of native copper and started experimenting with it: putting it into a fire, in water, striking it with stone hammers etc.
For a long time, both stone and copper tools ware in use, but as people experimented with copper (and other metals they found in the ground) it became obvious that metals could be shaped and combined more easily (creating alloys, like bronze). At some point, the majority of prehistoric people stopped using stone tools and switched to metal. This is how early metallurgy was born.
For example, copper was used for ceremonial purposes in the prehistoric city of Mehrgarh, somewhere from 7000 to 5500 BC. The ruins of the city are located in Pakistan. In Serbia, a copper axe was found, from about 5500 BC.