It is sometimes said that James Watt invented the steam engine. This is not quite true. A number of people had produced steam engines of sorts. Watt took the steam engine design of a man named Thomas Newcomen and made it much more efficient. This was Watt’s major contribution to the Industrial Revolution.
For a detailed explanation of how Watt improved on the Newcomen design, please follow the link below. For our purposes here, suffice it to say that Watt introduced a number of features that allowed the steam engine to produce the same amount of power with the use of less energy. He did this through such innovations as insulating the cylinder in which the piston moved and adding a separate chamber in which to condense the steam back into water.
Improving the steam engine was a major step in the Industrial Revolution. Steam power was the first type of power that could drive machinery anywhere and at any time without the use of animals. It was therefore more versatile and reliable than wind or water mills.
When Watt invented a way to make a steam engine turn things in circles, he helped the Industrial Revolution even more. This allowed steam engines to be used for something other than pumping water out of coal mines.
Thus, Watt contributed to the Industrial Revolution by making steam power much more useful for driving machinery.