Bank money is a medium of exchange consisting primarily of checks and concepts. In a fractional reserve system, money is created every time commercial banks lend and receive deposits.
Through the money creation process, a bank set aside a portion of savings, say 20%, as a reserve requirement. The rest, the bank can lend it to the debtor. Debtors, for example, use loans to buy cars. The car seller receives the money and then saves it in the second bank. The second bank then sets aside 20% of the savings and lends the rest.
The process continues and creates a multiplier effect of money. We can calculate it by the formula: 1 / Reserve requirements ratio. So, with Rp100, it can double to Rp500.