It owes far more than that - that's only the debt to China. And they certainly do have that much - it's a BIG country, and having some dollar investments helps their exports stay competitively priced, so it's a strategy that works for them. The total US national debt is more like $21 trillion.
It's all done by US Treasury bonds, notes and bills. Anyone can buy them as an investment, including you. And countries all over the world own them. (We in the UK are the 5th biggest foreign owner.) So do US citizens and companies - it's a good safe investment as it's very unlikely that the US government will go bust. It's a common strategy for pension funds - normally they might invest your money in stocks, but as your retirement approaches, they might move more and more of your money into safer investments like this Treasury paper, so you won't be left with nothing if the stock market crashes just before you retire.
Governments don't borrow from banks as you would do to get a loan - well, not usually. Being the government, it can fund itself like a company does by issuing stock or shares, with the difference that government bills have a set interest rate on them. Or they don't but they are marked that when they mature on a set date, after 90 days might be typical, you will get back a set amount more than you paid.
So the country doesn't have to pay anything back until the bills mature, and then it will undoubtedly issue more bills to keep the debt funded. As long as it can afford to pay the interest on them, the debt is affordable, and of course that is a lot less per year than $21 trillion. The latest figure is $240 billion (or $0.24 trillion), which is less than 10% of federal government spending, and that's factored into the budget and perfectly affordable.
Of course it would be nice if the government could actually afford all it wants to spend out of taxes, and then it wouldn't need to borrow by issuing more bills. It could even start paying some of the debt back, by repaying bills when they fall due and not issuing more. BUT that would mean higher taxes and/or big spending cuts. The government ends up HAVING to borrow to keep going without the voters squealing, and a sensible amount of debt is affordable, so running a deficit budget is normal. Governments everywhere do it.
The USA is actually above average in the amount of its national debt relative to the size of the economy. (Considering how keen it is on the government doing as little as possible, the government still manages to spend an enormous amount.) Japan has a debt over twice as much relative to the size of its economy and they're doing OK! Here in the UK, ours is slightly smaller than the US one thanks to some heavy spending cuts and continual reviews of how things can be done more efficiently.