What do i have to do to plug my 110 air conditioner into where my 220 window unit

You need a step down transformer, to convert 220V to 110V. You can't just plug the 110V A/C unit in directly unless it is clearly marked as being suitable for multi-voltage supply (110V - 220V input).

Such a transformer has to be of sufficient capacity to handle the current, or wattage, that will be required. The Frigidaire unit in your question is a 3.5 kW cooling capacity, so the transformer would need to be about the same, ie for a 10A supply at least. They are quite big boxes, about $120.

http://welectronics.com/TRANSFORMERS/step-up-down.JPG

You would put this in the roof or in a cupboard.

If the 220 volts a/c outlet is on a two pole circuit breaker by itself, no other outlets, and there is 110 volts available in your circuit breaker box, then you can move one of the wires from the existing two pole breaker to the neutral buz, where all the other white wires are connected, and replace the 220 volt outlet with a 120 volt outlet, the wire that was moved to the neutral needs to be marked white on both ends and connected to the silver colored screw terminal on the new 120 volt receptacle outlet. This is how you convert from 220 to 120 receptacle convenience outlet on a 220/110 volts electric service system.