Question

how does a steam engine do work

Answer 1

A fire where the coal burns. A boiler full of water that the fire heats up to make steam. A cylinder and piston, rather like a bicycle pump but much bigger.Steam from the boiler is piped into the cylinder, causing the piston to move first one way then the other

Answer 2

A fire where the coal burns.
A boiler full of water that the fire heats up to make steam.
A cylinder and piston, rather like a bicycle pump but much bigger.
Steam from the boiler is piped into the cylinder, causing the piston to move first one way then the other.
This in and out movement (which is also known as "reciprocating") is used to drive...A machine attached to the piston.
That could be anything from a water pump to a factory machine... or even a giant steam locomotive running up and down a railroad.

That's a very simplified description, of course. In reality, there are hundreds or perhaps even thousands of parts in even the smallest locomotive.

Hope this is helpful