Using relays

I have an assignment in which i need to turn an air conditioner and heater on and off through a micro controller...I believe i have to use relays... can anybody help me with the circuit...?
Also i wanted to ask that like turning on a cooler means starting its compressor,what is its equivalent for heaters?
Similarly in another assignment i need to control elevator motors by relays...

To pick a relay you need to know:
What is the maximun current that the air conditioner and heater consume?
How much current and voltage can the relay's driver circut supply to the relay's coil?
Is the MCU goes into a sleep mode while the appliances are ON or can he operate the relay's driver circuit as long as the appliances are ON?

You will need a transistor driver from the MCU to the relay to turn the coil on. Do not forget the diode across the relay coil.

Using a MCU to do this would mean you have already had other electronics classes right?

If it is a small AC/heat unit you can go with a solid state relay.

Digi-Key - CC1607-ND (Crydom Co. - PF240D25R)

is a bit expensive but will connect a PIC straight to an AC load.