Most money is created by the banking system. The demand for money depends on nominal interest rates and income. If the real money supply contracts interest rates rise. If the real demand for money rises interest rates rise. All things being equal, and in the long run, the price level is proportional to the money supply.
Money is a medium of exchange and usually serves as a store of value for individual agents.
It is intrinsically nominal. What matters is not money, but what you can buy with it. In fact, most money exists only in cyberspace - in bank deposits. Money is a gigantic con trick - but an enormously useful one. It may be the greatest technical advance of all time.