Bronze smiths make bronze by melting two different metals and mixing them. The two metals are copper and tin. Copper, by itself, is too soft to make tools of. (Have you ever had a copper bracelet? It dents every time you knock your hand on a door). Tin is too brittle: it breaks too easily. But if you mix a little tin into the copper, it becomes bronze, which is much harder and at the same time less brittle. It is more useful for tools and also better for making statues. (Early on, people tried mixing copper with other things like lead and arsenic, but tin works best.)
When West Asian smiths first began to make bronze, about 3500 BC, it was very expensive. Mostly people used bronze for weapons and armor. You could make a much better sword out of bronze than out of stone or wood. Bronze swords were lighter and sharper.
But soon Chinese and West Asian artists also began to use bronze to make bronze statues. As with the weapons, bronze is lighter than stone, and you can make statues in different poses with bronze than you can with stone. To get these bronze statues, the artists invented lost-wax casting.
When bronze gets old, and the air touches it, it corrodes (like iron rusting) and turns green, like these Etruscan greaves (leg armor). Once bronze got old and corroded, people usually sold it to a bronze-smith to melt down and recycle into new bronze things – that’s why we don’t have very much ancient bronze.