As in the money that is loaned out by your national bank? It is given to countries that are running a budgetary deficit and are seen as "safe" debtors. The relative safety of the debtor is based upon their ability to tax their population and make their interest payments. I forget the precise values, but they're in the defines file if I'm not terrible mistaken. While the loan is outstanding that country is paying interest. This interest is essentially additional income to the pops that had invested in your national bank. Bankruptcies can happen and if your bank loaned to that debtor you'll receive a casus belli against that country.
One can also take loans from their own national bank. There has been some disagreement as to how effective such bond issuance actually is in the long term, but it is a strategy that I enjoy employing at times.