By definition, economic growth happens when a country's Real GDP goes up. The term usually refers to a sustained rise in the RGDP. This typically happens because of an increase in the resources available to an economy or because of advances in productivity (new technologies or techniques for producing things more efficiently).
When economic growth happens, it usually causes an increase in the standard of living available to people in the economy. They are able to purchase more goods and services. We can see this happening in China today as economic growth allows people to eat more of what would have been luxury foods and to afford things like cars.
On the bad side, economic growth can lead to things like pollution and overcrowding of housing stock and roads. Once again, this has been visible in China. China has, for example, terrible pollution problems in places like Beijing.
So economic growth helps people live better lives, materially speaking. But it can come with some costs as well.