The government spends it one what it thinks it needs to spend money on. The money is now due back from the tax payers. That is not in the first place a problem, since the money is out there in circulation. But, the bank wants the money back with interest. The central bank is not the only one that can create money.
Any bank can.
Regular banks create money by being allowed to lend out a certain number of times more money than they have deposits for. For example, if there is 1 million in the bank, it can lend out 10 million, thereby creating 9 new millions. Regular banks also charge interest. Meaning that, no matter how much they create, they always need MORE back. Technically speaking, that is impossible.