Okay kiddo, a scotch marine boiler is like a big pot that we use to make steam. It's called a "marine" boiler because it's often used on ships, and "scotch" because it was first made in Scotland a long time ago.
Inside the boiler, there are two big areas called the "firebox" and the "combustion chamber". The firebox is where we burn fuel, like coal or oil. This makes hot flames that go up into the combustion chamber. In there, the heat from the flames makes the water in the boiler turn into steam.
The steam is really important because it can do lots of jobs. It can turn a big turbine to generate electricity, it can power engines on boats, and it can even heat up buildings.
But we have to be really careful with scotch marine boilers, because they get really hot and can be dangerous if they're not looked after properly. That's why there are always trained people around to make sure everything is working the way it should.