Long ago, the world's economy was based on the bartering method. The value of a particular item, was measured by it's worth in exchange for other items. But, this system had it's obvious limitations. If you had nothing of value to exchange, you had no way of obtaining items you needed. This created the need to establish a more acceptable way of buying and selling early in history.
In various cultures and economies, anything could be considered valuable as long as there was a need for it. In some cases items such as animal pelts, corn, wheat and even hand made items were exchanged to obtain other much needed items.
