I recently added freon to my fathers 1997 chevy lumina,the inlet is right under and near the rectangle shape air filter.you may have to remove air filter for access.it will take 134-a freon,buy a kit with hose that has a brass end this works better than the hard plastic ones.read directions carefully and make sure you choose the right valve.there is a _low and a _high pressure inlet or valve they are near each other. Do not put in the wrong side it could damage your hand and or face use caution and be safe.if you are not sure see mechanic.
Go to your local auto part store, and buy a can of r134 freon. You will also need a hose to attach to the can, and to the low pressure port on your a/c system. If I were you I would get one of those cans that comes with a hose with a pressure gauge on it, so you know when to stop adding. Too little or too much is bad for the compressor. It is the tall Arctic Freeze freon can. And when you use that can up, the hose is removable, so you can keep the gauge.