Someone else here posted this and told me I could copy/paste it:
There are currently three styles of vaping:
Pod mod: Low power, low juice usage, tends to use really high nicotine levels to make up for the low power.
MTL (mouth-to-lung): Sort of a middle-of-the-road option. Gives you a bit more power, uses a bit more juice, and the juice is generally at a slightly lower nicotine concentration.
DL (direct lung): Big clouds. A lot of power, a lot of juice, but since you're going through so much juice it usually has a lower concentration of nicotine.
Moving on to MTL kit:
You'll want a mod, which is the power source and holds the battery, and a tank, the thing on top you put the eliquid in.
Tank
Tanks hold the eliquid and the coil, which vaporizes it. Coils are replaceable and generally last around 1 - 3 weeks. Tanks are designed either for MTL or DL. Some can do both, but usually not well. The tanks mentioned above (Innokin Zenith or Zlide and Aspire Nautilus GT) are excellent MTL tanks, and probably what you want to get.
Mod
Mods can usually be used for either MTL or DL. Some lower-powered mods don't have enough power for certain DL tanks, but I won't go into that unless you want more information. The big decision with a mod is whether you want an internal or integrated battery mod or a replaceable battery mod. With an internal battery mod, the battery is part of the mod and you usually charge it by USB. With a replaceable battery mod, you take out the batteries and charge them in a charger.
The advantage of replaceable batteries is that they're replaceable. Batteries only last so long - often a year or so - so when the battery in an internal battery mod wears out you need to replace the whole mod. With a replaceable battery mod, you just replace the battery and keep using the mod. Some people also prefer being able to swap batteries instead of having to recharge the mod.
