Replying to Just got an e cig and its awesome. Also some questions, + k for answers

I got the aquavaporcig 510 at the behest of barefootin fiends urging and its sick. It hits so hard and gives you a buzz like smoking a hookah. My question is what is the best way to get refills? Should i order more cartomizers online or should i use the liquid that csme and refill the cartomizers myself? Also it came with like 4 plastic empty tubes. What are these for? Also how will i know that a cartomizer is empty so i dont keep burning it and burn out the heating element?
Thanks and +k for answers