Look it up on ebay Karennina - easier to see than tell you.
Basically it's a plastic tube, some look just like a ciggie, with an atomiser cartridge/battery heater. You have nicotine cartridges that go in them & they heat the nicotine & you inhale nicotine vapour that is scented like tobacco. It gives off harmless vapour that looks like smoke so you apparently feel as if you are smoking.
However it contains none of the 400+ carcinogens & extra additives the ciggie companies put in to keep you hooked - so hopefully you cut down use.
I've just ordered one off ebay - hopefully it'll stop us buying ciggies. Sometimes you just need one & then the willpower goes & you have to smoke the rest of them :-(