Keep in mind - this is macro stuff, and has nothing to do with your test. I'm glad you're interested, though! :)
Inflation is a weird thing. Technically, it's a decrease in the value of your money - something that cost $1.00 last year costs, on average, $1.03 now (at 3% annual inflation). This is a good thing - it allows for growth. But our government has a fear of inflation almost as much as a fear of deflation (like during the Depression).
If inflation rises too fast, the government (the Federal Reserve, who controls our money supply) will step in and cut down on the money supply (usually by changing interest rates) in order to get it under control. There's a fear that hyperinflation could occur - and that's talking about something like 1000% annually (which has happened in the past in other countries).
If we just printed $6 trillion to pay off the debt, it limits the scarcity of money and cuts the value. If there are 6 trillion diamonds on the ground, having one diamond won't mean anything. It's the same idea. So - your money becomes worthless. Literally, if they print that much at one time.
The money is owed to people who have loaned money to the government in the form of Treasury bills & bonds. Those people would get some of that printed money in that case, but it would be limited - $1000 here and $2500 there. As the value of the money people had would drop, prices would rise - and probably quickly. Wages would not keep up with the prices, and we would see layoffs as companies could not keep up with their costs.
And with such a huge influx of money at one time, this would happen quickly.
Only a portion of the money is owed to US citizens - we do owe other countries, also, so the currency would be leaving the country, which is a whole different story.
'Course, this is all theory and may not happen at all. But I don't think that politicians are willing to take the chance.