It’s just taking advantage of the change in matter state. H2O expands ~16,000 times it’s size when it boils from liquid water to gaseous steam. That increase in size means it wants to go somewhere else, we just control where it goes and it’s relief valve happens to be going through a spinning wheel with magnets on it, inducing currents in the coils of wire around the wheel.

Yes it’s way more complicated than that, but it’s the best way we have of turning heat into electricity, so it’s what we use. With the primary exception of solar, nearly every form of power production is using heat energy to indirectly spin a wheel.