Your question is not clear...
takes the heat away from engine low coolant??
The engine overheats and parts can melt, crack, even explode (massive expansion due to heat.)
The engine's thermostat controls the engine coolant temperature. The temperature control inside for the heater controls the cabin heat.
heat It transfers engine heat from the coolant to the air inside the car.
Transferrs heat from the engine to the radiator the to the air it also transferrs heat to the heater core for warm air inside the vehicle
thermostat
You are probably very low on coolant. If so you have a leak somewhere. Have it check by a mechanic now before you damage the engine if you haven't already.
why does my Honda civic overheat and doesn't heat at all
The engine works hard and produces a lot more heat than when the car is driven on a leveled road. The car is usually driven slower on the uphill and there isn't as much air cooling the radiator. But the main reason it overheats is that the cooling system is malfunctioning.
A car engine works by burning a fuel and air mixture releasing heat into the engine making it hot. The workings of the engine also involves friction which creates additional heat.
As a "heat engine", a car engine must rid itself of heat to continue. Efficiency of the heat engine depends on the difference in temperature; therefore, as the temperature outside reaches the temperature inside, the engine stops.
You could be low on coolant, a stuck thermostat, engine fan not coming on for starters. If still overheats, I would recommend taking it to a Subaru dealer.