A video looking at way you can't simply print money to pay off debt. And what has happened when countries have tried to! And for that matter why a country having debt isn't necessarily a bad thing. The only reason the US has the most debt is because the US dollar is considered the most trust-worthy currency and other countries see the US as a safe place to put their money.
It would be worse it countries started buying debt of other countries and stopped putting into the United States. The debt may be a lot but it's actually not something that's an issue. The US will never 'pay-off' its debt because that's not how it works.
National debt only becomes an issue if GDP isn't growing, which it is. A more accurate way to see when the debt is an issue is the debt-GDP ration. In which the US is fine in that respect. Whereas Greece and Japan have debt-GDP ratios of over 150%, which is bad.
Also, keep in mind that the US owns debt of many other countries. In fact, for every $1 of US debt, the US holds $0.89 of foreign debt.