A window air conditioner is not a replacement for a central air conditioning system. Trying to use multiple window air conditioners to cool an entire house can be a very costly mistake. A central air conditioning system is meant to cool your entire home in most cases, or at least a large portion of it. Their hardware, filters and ductwork are meant for the larger jobs. Individual window units are not.
Start by making sure all windows in the area you want to cool are closed and properly sealed. Then close any doors you can to isolate the target area from the rest of the house. This will help to prevent the cool air from leaking through windows and doorways to other rooms or the exterior of the house. If you find that air leaks between the bottom of a door and the floor, you can find inexpensive cloth stoppers that can be placed at the bottom of the door to prevent air from getting through. Or, for a quick fix, you can try a bath towel.