Super-simple way to explain it:
Rich people put money into banks, which lend it to governments; governments pay money and interest back to the banks, who pay interest back to the rich people: rich get richer.
So now the governments are saddled with debt? What do they do with the money they got in exchange?
They use it to buy stuff from contractors. The contractors work for companies that are owned by rich people: the rich get richer.
It's a dirty system. Our governments borrow money from the elite (with interest!) so that they can spend that same money at the companies owned by the elite (for profit!) It's a dirty, dirty system.