You should read the guide and other stuff in the DIY section
DIY e-liquid
You don't have to add flavoring to prefilled cartridges. You add
eliquid to keep using the same cartridge. And if you have a ton of money and buy all the cartridges you need and never get caught short, then you don't have to refill them.
eliquid flavoring is pro food flavoring (minus some flavors not safe to vape) which is mixed with nicotine (which is in PG or VG) plus more PG and/or VG and sometimes plus a bit of distilled water to loosen the flow of high VG liquids, plus optional diluted splendex and/or ethyl maltol sweetener, and that makes an elqiuid. There are calculators to help figure out the amounts of each but the amount of flavoring and sweetness is figured out by the mixer, using any available suggested percentages for that particular flavoring as a starting point.
But most people just buy premade eliquids in their desired PG/VG ratio (or a thickness they know they like) and nicotine level.
PG is thin and lets through the most flavor, the most nicotine TH and the most nicotine irritation
VG dulls everything PG lets through and adds thicker visible vapor
In stuffing cartomizers I like thin juices - PG juices with 20% VG or less
In
tanks and reservoir cartos 30% or less VG works well and some thicker juices may work OK
on a normal atomizer you can use any PG/VG as long as it flows at least as fast as you vape it
