You can refill your 1987 VW air conditioning system from the low pressure port on the air conditioner compressor. Connect your Freon bottle to the low pressure port and release the Freon into the system.
A Freon system on a 1993 Honda Accord uses a valve on the A/C hardline where a user can connect a A/C refill can. Following directions on the refill bottle will show how much Freon is needed to pressurize the system.
If you look under your hood somewhere either on the front bumper itself near the radiator or right under the hood should be a sticker usually yellow orange or white that tells you how much freon and what type to use. Normally a passenger car takes 2 to 2 and quarter pounds of freon.