Imagine you traveled to a foreign country, and the only two places you could exchange your dollars for some local currency were the hotel desk and the bank.

Let's say that the hotel bought and sold dollars for 110 currency units each, and the bank bought and sold dollars for 120 currency units each.

In theory you could go back and forth between hotel and bank, buying local currency at the hotel and selling it back into dollars at the bank.

If you did this all day long, by the end of the day you would have a stack of bills left over. This is a conceptual example of how properly understanding exchange rate quotes can help you create wealth.