Our planet is comprised of some 193 countries using 164 different currencies!!
If you have ever travelled to another country using other than your home country's money, you have probably exchanged what was in your pocket for the currency of that country so you could buy things while in that country. When leaving to come back home, you probably exchanged what you still had of their money back into yours, too.
If you had paid attention, you might had noticed that the amount each currency was worth in terms of the other one was different each time by a small amount.
This is the extent to which most people are exposed to exchanging currencies- but there is SO much more to this than that!
The global currency exchange began in antiquity as traders and merchants began buying and selling across national borders.
This was done by "the money changers" (yep- there is a passage in the Bible where Christ expelled the same from the temple for doing just that in a holy place instead of over the Internet!!) Mathew 21:12
Today, all of the transactions are computerized, and one need not actually be in another country to change their funds into that country's money, but there is still a rate of exchange, and a small fee is still charged by "the exchangers" for making the switch, too!