There's a difference between money and currency. Currency is what you have in your pocket or bank, money is what currency represents.
This is about the history of trade. Trading seems to have always existed - one tribe is better at making beaver pelts than a tribe downstream which excels at carving shells - so people bartered. When herds of livestock became trade goods, people needed something more convenient than 300 head of sheep, and they began trading in ingots of metal or valuable stones such as lapis lazuli. The ingots were at first copper, then bronze, then gold and silver. The ingots had a uniform weight (at least in certain trade areas), and eventually people realized that making coins out of the ingots was even better. That happened about 2500 years ago in Lydia, in what is now Turkey. Coins caught on really rapidly.