How the banking system works

"The funny thing about how a bank works is that it functions because of our trust. We give a bank our money to keep it safe for us, and then the bank turns around and gives it to someone else in order to make money for itself. Banks can legally extend considerably more credit than they have cash. Still, most of us have total trust in the bank's ability to protect our money and give it to us when we ask for it."
source http://money.howstuffworks.com/personal-finance/banking/bank.htm