How do you add coolant to a goldstar air conditioner

There are two lines leading into the unit, the high side aND THE LOW SIDE. tO ADD FREON you need to add a valve to the low side line. But if you have a leak that indicates that moisture is in the unit and you need to pull a valum to remove the moisture before ADDING ANY FREON. There are as last known three types of freon, R22, R134a and this last one I dont even know the name.