You mean into the window? Is it a window air conditioner?
If it is a window air conditioner all that is usually needed is some sort of mounting bracket to go underneath it. You can find 2 models at the following links which have a built in level to assure proper tilt for drainage of the unit.
Some tips from my site's 'Helpful Tips' section may also help:
When installing a window or through the wall air conditioner, it is important that it still be removable. It will need to be removed for repairs and the periodic maintenance that is required from time to time. It is also important that none of the air louvers on the sides be blocked. Reducing these air vents will reduce the cooling ability of the unit and can lead to premature component failure. Any failures caused by this will usually not be covered by any warranty.
To aid the flow of recovered room humidity from the front of the cabinet towards the rear, make sure that the unit is pitched so that the rear of the unit is 1/4 to 1/2 inches lower than the front.