The main concept of a steam engine is quite simple. The only problem with a basic steam engine is that it has limits and most of the time it can't spin gear or a paddle wheel.This is why there were many different variation of the steam engine, because you could modify them to fit whatever you needed power for. The most commonly used engine concept at the time was invented by James Watt. The way this engine worked is water was heated in a coal-fueled boiler until it produce steam, then the steam is forced into a piston cylinder, then the cylinder was pushed up and as it reached the top it opened a valve which released the steam, then the cycle was repeated.the problem with this simple design is that it only moved a piston up and down. Inventors found out that if you connected an arm to a moving wheel that the wheel would turn when the piston moved up and down. Robert Fulton used an arm connected to a large gear that linked to a smaller gear and then finally to the paddle wheel. This was only one type of steam engine. Steamships usually used twin gears that moved with the piston; these gears were then connected to propeller that spun. This design is the closest to the modern-day boats.Steamboats were usually composed of lumber, steel for the engine, and coal for the fuel source.