2002 Pontiac Grand Am GT Cooling system and heater

I have a 2002 pontiac grand am gt. Start the car the two cooling fans do not come on. The engine will overheat and water comes out of the overflow tube, low coolent light comes on etc. Turn the heater on and the cooling fans come on. Let the car cool down and then start it again with the radiator cap removed, heater off and the fluid level will rise and fall as the engine heats up. Again the fans are not on and car will overheat. Lastly, with the heater turned on, air comes out of the vents but does not heat up.

I was told that the fan switch and/or relay could be the problem. Can you tell me where they are located? And where is the heater core located, possible heater problem?

Thanks,
Kevin Venturella