Sounds to me like your using cartomizers, good choice

You just pop off the white cap by inserting a paperclip into the middle hole and pry around it. There is another silicone piece in there to take out. Just put some drops on the filler, avoid the middle and put both pieces back on. Usually takes bout 15 to 20 drops for a dry cart. Don't overfill you'll get liquid in your mouth! Try searching the "spin method". It really packs alot of drops in there and brings the flavor out.