The Industrial Revolution was a time in history when (since we are talking about Britain) the British economy became industrialized. What this means is things started to be made more and more by machines. In the past, things had been made by people working by hand. Power had come from water, wind, or the muscles of people and animals. Now, power came from steam engines that drove machines that were used to make things.
The Industrial Revolution had a tremendous impact on British society. The following are some of its major impacts:
It caused massive increases in the size of British cities and the percentage of people living in those cities. In the past, most people had lived on farms. Now, they came to the cities, in part so that they could get jobs in the factories that were springing up.
It caused a change in the way people worked. People had previously been, in general, their own bosses. They worked when and how they wanted to. This changed when they went to work in the factories. Now, they had to do what their bosses told them. Their bosses determined when, how, and how hard they worked. This made workers much less happy with their jobs.
It changed the British class structure in two ways. First, it created a huge working class of relatively poor people. In the past, there had been landlords and peasants. Now, the urban working class became much larger. Second, it reduced the wealth and the importance of the old aristocracy. In the past, land was the main source of wealth and aristocratic landlords were the wealthiest and most important people. Now, the rich elites were the capitalists who owned the factories.
In these ways (and others) the Industrial Revolution fundamentally changed British society.