Oh man, i highly suggest reading everything you can find on battery safety. You bought a good charger and batteries, so dont worry about that. Marrying batteries basically means they need to do everything together. They must charge together and discharge together. Once you use a married battery in a single 18650 mod, whether it be a regulated or mech mod, they are no longer married and cant become remarried. Mark them, something simple like writing a number or letter on them to make sure you know they are married at a quick glance. Marrying batteries ensures they "age" together if you will. They will have the same number of charging and discharging cycles on them, making sure one isnt stressed more than the other. Im not the person to give you the most indepth explanation so please read everything you can find on this subject and battery safety in general.