Actually, reactor coolant is cooling water. It circulates through the reactor carrying away the heat. It is driven by real kick ass pumps through the reactor and forced through the inside of 12,000 steam generator tubes in a steam generator and back to the pump suction.
The secondary cooling water is on the outside of these tubes in a lower pressure system and carries away the reactor heat by flashing to steam which is usually used to run steam turbines which generate electricity by turning a generator.
The used steam from the turbine is condensed by flowing onto the outside of tubes in a condenser and turns into water which is pumped back into the steam generator, again by kick ass pumps.
The third cooling water system is the water sucked from the ocean, a river, a spray pond, a cooling tower system by really, really kick ass pumps in some cases. It goes through the inside of the tubes in the condenser and then back to the source.
"Reactor Coolant" refers to the water that actually flows through the reactor. All the other systems cool other things.