A traction engine is like a really big toy car that doesn't run on gas, but rather on steam. Think of it as a machine that can move and pull things, kind of like a horse, but is made out of metal and is powered by water and fire instead.
Imagine a big metal box with wheels, and inside the box is a furnace where you put coal to make a fire. The fire heats up water inside the box, turning it into steam. This steam is then pumped into a large cylinder, which makes a big piston (like a metal rod) move back and forth. This back and forth movement is what makes the machine move forward.
The traction engine was first invented in the 19th century and was used for lots of different jobs like plowing fields, hauling wagons, and powering machinery. But today, they are mostly used for fun as a neat piece of history to look at and play with.