you tube actually has some great vids on doing AC work. Id cut out one of those 20% off @ harbor freight coupons and pick up a cheap manifold set if you dont have one. You'll also need the attachment that screws onto the freon can and punctures it.
now sure what state your system is in or why its discharged to give any further advice
If you do not know what you are doing, I'd recommend paying someone that does. Over charging the system can be worse than under charging. Holding the can the wrong way can effect the charge (gas/liquid or low/high side).