If you've never tried any carto's before then I think you are in for a nice treat! They're super simple to use and fill.
Pop the little end plug off and tip the carto at about a 45 deg angle and slowly drip your
juice in around the edges. On the first fill it takes a little time because the filler doesn't like taking in the
juice but after that initial fill it will suck the
juice in much faster. Don't get any juice in the center air tube as this floods them. If you do get some juice in the center tube then just blow it out after your carto is full. You can tell when the filler material has absorbed all it can take when it looks slightly slushy but doesn't poor out if you turn it upside down. Put your end plug back on and vape away! That's it!
Oh... one word of caution with any type of carto including these dual coils. ALWAYS keep them wet, especially if you are vapping thicker juices like Malty that has a lot of VG in them. The very moment you taste anything burnt or slightly off stop and top it off again. There is no danger to yourself but if you burn them dry enough times all your juice will taste funky and there's nothing you can do other than trash it and grab a new one. As with all cartos, it may take you a little time to get the hang of them so don't give up on them if you have any troubles. Flooding them was my biggest learning curve.
Good luck and enjoy!