To spell this out a bit more, imagine you and I are the only producing, buying and selling things in the economy.

I grow five turnips for sale, you grow five carrots for sale. The government has printed £10 and we each have half of it. I want five carrots and I give you £5 for them. You want five turnips and give me £5 for them.

Now imagine the government gives each of us another £5 so we have £10 each.

What often happens is that an increased supply of money decreases its value. So now what happens is that I charge you £2 per carrot and you charge me £2 per turnip.

That's inflation. Now inflation has good and bad points - or rather it tends to benefit some and harms others. A careful increase in the money supply to help pay off debts can be a good thing for a country. The benefits can outweigh the costs. It doesn't automatically lead to runaway inflation.

There are also cases where inflation doesn't happen. Let's say I've got an unused field and I could grow more carrots, but you don't have the money to buy them. In this case the government creating more money can help the economy.

Knowing when this is and isn't the case is one of the big challenges for economists, central banks and governments. The US in the years right after the financial crisis is a good example: money creation stimulating economic growth and not driving inflation. Those conditions have probably changed now, though, and most developed countries are trying to restrict the money supply.