Accept Deposits / Make Loans
At the most basic level, what banks do is fairly simple. Banks accept deposits from customers, raise capital from investors or lenders, and then use that money to make loans, buy securities and provide other financial services to customers. These loans are then used by people and businesses to buy goods or expand business operations, which in turn leads to more deposited funds that make their way to banks.
If banks can lend money at a higher interest rate than they have to pay for funds and operating costs, they make money. An illustration of this very basic concept can be found in the old "3-6-3 Rule. " a tongue-in-cheek "rule" that said a banker would pay out 3% for deposits, charge 6% for loans and hit the golf course by 3 p.m.
Banks also provide security and convenience to their customers. Part of the original purpose of banks, and the goldsmiths that predated them, was to offer customers safe keeping for their money. Of course, this was back in a time when a person's wealth consisted of actual gold and silver coins, but to a large extent this function is still relevant. By keeping physical cash at home, or in a wallet, there are risks of loss due to theft and accidents, not to mention
the loss of possible income from interest. With banks, consumers no longer need to keep large amounts of currency on hand; transactions can be handled with checks, debit cards or credit cards, instead.
While banks do not keep gold or silver bullion as currency on hand anymore, many, if not most, banks still maintain vaults and will rent out space to customers, in the form of safe deposit boxes. This allows customers to keep precious or irreplaceable items in a secure setting and gives the bank an opportunity to earn a little extra money, without risk to its capital.
Act as Payment Agents
Banks also serve often under-appreciated roles as payment agents within a country and between nations. Not only do banks issue debit cards that allow account holders to pay for goods with the swipe of a card, they can also arrange wire transfers with other institutions. Banks essentially underwrite financial transactions by lending their reputation and credibility to the transaction; a check is basically just a promissory note between two people, but without a bank's name and information on that note, no merchant would accept it. As payment agents, banks make commercial transactions much more convenient; it is not necessary to carry around large amounts of physical currency when merchants will accept the checks, debit cards or credit cards that banks provide.