Banks basically take your money, lend it to your neighbor,
charge her a steep interest rate for the use of the loan,
keep most of the interest for themselves, and then pay you
what little is leftover.
That's a highly simplified analogy, but it reflects the general
concept. For a more detailed explanation, check out the following:
Banks borrow money from individuals, companies, and sometimes
even governments, then turn around and invest the money in
securities or through private loans to make a profit.
You can't exactly go into a central bank and ask to open a
checking account. These are the big guns that establish national