Focusing on the majority of the US money supply, the method (Fractional Reserve Banking) is as follows:
The Federal Reserve Notes and equivalent Federal Reserve Deposits (mentioned above) are deposited in local banks or to their credit at one of the 12 Fed banks. These funds serve as the base of bank loans, which require a 10% reserve. For example, if $1,000,000 of Federal Reserve notes or Fed deposits are entered on the books with the Fed to the credit of a bank (usually the bank of the person or company which just sold the Fed a Treasury bond/bill or note), that bank may loan all of that money out (at interest), except for 10% which is kept as its reserve. Thus $900,000 in this example may be loaned out by that bank.
In the usual case, the borrower of the $900,000 will not, of course, keep the money under the mattress, rather, it is deposited either in the same bank or in others. This $900,000 in new deposits may then be loaned out at interest by these banks, except for the 10% reserve. Thus $810,000 is loaned out a second time ($90,000 of the $900,000 being retained as reserves).
The newly loaned $810,000 is then deposited in these or other banks, allowing them to lend out $729,000 a third time (retaining 10% = $81,000 as reserves), and so on. This process gets repeated over and over, each time the lending bank(s) retains 10%. It takes a series of 66 loans to reduce the funds available for relending to less than $1,000 by retention of 10% each time as bank reserves. In actual practice, due to numerous exceptions to the 10% reserve requirement, banks may lend the money even more times, resulting in even more money being created by them.
Thus, in our example, an original purchase by the Fed of $1,000,000 in Treasury bonds on the open market, by a series of deposits and loans in one or more banks, results in an expansion of the US money supply (via bank accounts simply created as loans by the lending banks) by a factor of 10x. After the process is completed, the total money in the US economy has been expanded by ten million dollars ($10,000,000), in this example. The Fed got to create 10% of this total, and private banks the other 90%, to lend at interest. In each individual bond purchase by the Fed, not just one bank profits from this scheme, rather the banking system as a whole does. However, in practice, the 4 largest international banks get roughly 80% of the profit, leaving the crumbs (still million$) to the smaller banks in your community.
What did the banks do to obtain this right to lend, relend, and relend again and again the same money (less 10% reserved each time)? Nothing, except lobby and mislead the public, the majority of Congress and President Wilson to think they were supporting legislation to reform banking to a more just form under the Federal Reserve Act of 1913. They continue to hide, obfuscate and mislead the public, to the same purpose, using media they purchased for this purpose, and corrupting the political system in the process.
This critically important piece of legislation – the Federal Reserve Act of 1913 - had to be disguised to accomplish the bankers' scheme, and so it was. That story is contained in the video/DVD, The Money Masters: How International Bankers Gained Control of America.