buy the can refrigerant with the adapter already on it from pepboys or wherever and start your car with the ac running on high. on the front passenger side of your car, you will see 2 metal lines with blue caps on it. unscrew the cap with the "L" on it. DO NOT TOUCH THE ONE WITH THE "H" ON IT!
the "L" one is your low presure line and that is the one you need to use to refill. just attach the connector to it and let the can empty into the system. you might want to buy a compression meter to make sure you are not overcharging/undercharging the system.