Tanks, Pods, and Coils
Mouth To Lung (MTL) tanks have a restrictive draw that simulates smoking, and can be used with traditional e-liquids or new nicotine salts. Direct To Lung (DTL) tanks have a largely unrestricted draw that allows you to inhale directly, without first having to draw in a mouthful. They have a far greater power demand and produce a much larger cloud, so generally should only be used with nicotine levels as high as 6mg.
Most tanks have multiple coil options with different resistance levels and recommended wattage ranges - the best measure of how much vapor will be produced: the lower the resistance, the more power can be used, and the larger the cloud made will be.