In my first and second part, I had explained what money is and brief history of Money. Money and currency have all the same characteristics except money is a store of value, whereas currency isn't. A thousand dollar bill won't buy the same amount of goods that it used to buy 30 or 40 years back.
Before Money was introduced into human culture, the only way to trade goods was through bartering. Barter system relies on the principle of coincidence of wants; you hope that you will find someone that you need and who wants something that you have at the same place and at the same time.