All 18650 batteries are 3.7V nominal 4.2V max.
You mod has 2 batteries in series which means it has 8.4V max available.
You mod is regulated, which means it can raise of lower the voltage to what is needed, based on the wattage you have chosen and the resistance of the coil.
With a pair of 20A CDR batteries you can raise the wattage up to around 120W no matter the resistance of your coil.
Welcome aboard. @nightshard already covered everything you need to know