were do you add the freon?

Not freon anymore, they now run R134A for refrigerant. You can buy kits that connect into the low pressure A/C line to recharge it, but I'd personally recommend bringing it to a garage to have and A/C service done. They can preform a pressure test to confirms there's no leaks and it will make sure the system is properly filled to the right amount

Where is the low pressure A/C line?

Left side of he engine compartment the smaller of the two A/C line fittings should be a blue cap