A steam engine is a mechanical device that creates energy from steam, and this engine can be used to power something large, like a train or boat. The first mentions of a steam-like engine are from the 1st century, where there were several devices that could weakly power objects like door-openers and organs. However, these were unique designs used only by individuals, and were hardly reproducible or useful for most people.
Over the course of the 15th-17th centuries, several other steam-powered devices were either designed or created. One of the earliest of these was by Leonardo da Vinci, who created a canon powered by steam. However, none of these were strong enough to make great strides or be used by many people during the time they were thought up.
However, in the 1700s, the development of a commercial steam engine began. Thomas Necomen combined several ideas and previous designs and combine them into one single idea to create a steam engine that could pump material in a mine in 1712. To create this engine, Necomen combined a vacuum and pressurized pump created in 1654, device created in 1663 that could collect steam, and a piston/cylinder combination. The advancement of all of these individual pieces of technology was what allowed Necomen to create the first steam engine.
Necomen's pump worked by collecting steam, then cooling the steam with water, which created a vacuum. This vacuum would push down the piston. This piston was attached to a chain that could pull a beam. This would cause the pump to go in one direction, resetting the device, allowing it to pump back and forth. By 1735, nearly 100 steam-engines were in use around Europe, and by 1800 there were as many as 2000.
Other scientists, including one by the name of James Watt, continued to make improvements upon the steam engine design. He found that in the Necomen engine, nearly 80% of the steam was not used and just went to waste. He wanted, and succeeded in improving this design. Other scientists followed suit, and the steam-engine became a machine that is still used today to power large machinery like boats, and trains.