This is just going to be in basic terms, but macro economics and world debt is nothing like your own personal household economics and the loans you owe, so to try and equate them is disingenuous and is what causes the confusion.
A country isn't 'lent' money by another country. If our country wants to borrow, we issue bonds that are bought on the money market (By individuals, companies, pension funds, countries etc). Money can be created out of thin air by central banks by using the fractional reserve system and then it is just eroded away by inflation over time, all you have to do is service the interest until the debt becomes negligible.
A country (especially one who controls it's own money supply) can run a deficit, every year, forever....as long as there is enough growth to outstrip the level of inflation. (not that it matters in the short term if that doesnt happen either, we are looking at the very long term picture.) In fact, in economic terms, running a surplus is a very inefficient and undesirable thing to do - which is why we don't do it!
Just think, we borrowed 2 billion pounds in 1914 to fund world war 1. Which in 1914 was an enormous amount of money. We still haven't paid it off, but now in 2015 2 billion pounds is nothing in comparison to what it was and the interest we pay is negligible - because inflation has eroded the debt away.
We will never, ever pay off the £1.5 Trillion pounds our country owes within the current time frame, but in 1 - 200 years, £1.5 Trillion will just be chump change
That's not to say our deficit got to levels we were comfortable with after the financial crash (nothing to do with labours spending) and it was prudent to get it back under control, but the methods of doing it are just ideological rather than economic and the Conservatives mantra of aiming for this 'surplus' to pay off the debt is just pandering to simpletons.