The traditional theory is that in hunter-gatherer societies everyone had to work all the time to find food and other necessities of life, but when agriculture was invented, societies were richer because it didn't take everyone to provide food. This theory is controversial today. Jared Diamond (the author of Guns, Germs and Steel, if you ever heard of that), wrote an essay called 'Mankinds Biggest Mistake' in which he contends that hunter-gatherers spent less time finding food than later agriculturalists did in growing their own food. I'm not sure which side is true.
But back to the original theory. Agriculture brought about civilization. When people stayed in the same place for generations, they built villages and towns, they needed more specialized skills. Not everyone had to be involved full-time in providing food, so crafts flourished. People learned to make baskets, pottery, tools, and other useful things. Carpenters were needed to build homes or shelters. It became necessary to build governments, so politicians evolved. Armies were needed for protection.
Hunter-gatherers had these things, but under civilization people were able to specialize in these jobs in a way they never could before. And this helped civilization develop further.
