Basically, an e-cig or vaporizer heats up a liquid (known as e-juice or juice) that is basically vegetable glycerin or polyglycine (sometimes both) plus artificial flavoring (usually baking type flavoring) and nicotine. The liquid is vaporized and inhaled just like a cigarette would be. The big difference is that you don't have the 500 something other potentially toxic chemicals that are found in analog cigarettes. Since nicotine really isn't that harmful (no more than caffeine) and not a cancer causing agent you are simply supplying nicotine to your body in a different way and avoiding a lot of the negatives of smoking. E-juice is also available in a bunch of different flavors and nicotine strengths. I typically "vape" butterscotch , RY4 (has a sort of maple flavor) or 555 (has a sort of nutty flavor). The vapor that is exhaled is water vapor and is typically odorless. So you don't smell like smoke and you can "smoke" just about anywhere. I've used mine on a plane and in plenty of restaurants.