When a bank issues debt, the money is created 'out of thin air'. When the debt is paid off, that money is destroyed. However usually more debt is being created than redeemed as things go on, so the total money supply increases (this is a good thing, as it allows the economy to expand).
Various regulations and central bank market interventions (quantitative tightening/easing) control this process, which thus can be induced to 'print money' if the government wishes - assuming they have a sovereign currency.