At 6000 BC, Barter System was introduced. Here, Commodities were being exchanged between one person to another without any currency. But, That was not suitable for both parties. One can’t buy rice with exchange of horse.
Then gold was medium to exchange of commodities. Again, it was difficult for tribes to carry gold because it was heavy & unsafe.
Finally, Currency note took that placed which is still we are using conveniently in our own country.
Forex came which made very convenience for the foreigner to buys & tours in different countries.