Although electronic cigarettes can be made in a variety of forms and shapes, they all have the same basic components. The mouthpiece (also known as the cartridge) is a small disposable plastic cap that is attached to the end of the tube, and when they are screwed together they look like a real cigarette. Within the mouthpiece is an absorbent material saturated with a liquid nicotine solution. Suction causes air to flow through the hole in the end of the mouthpiece to bring the vapor into your mouth. The only heated part of an electronic cigarette is the cartridge which contains the liquid nicotine. The heater runs off a lithium-ion battery, which can be recharged as often as you want in a wall socket or via an-car charger. It depends on the type of battery used, and how often you use it, but you can expect the battery to last for a least a couple of days before needing to re-charge it.
As for the nicotine solution, you can refill the cartridges when they run out. The liquid normally contains some kind of flavoring, and consists of nicotine dissolved in propylene glycol and / or glycerin. Both of those substances are common food additives, and are not considered harmful to your health. Different concentration levels of the nicotine solution allow you to choose the amount of nicotine you want to consume. Concentrations range from low (4mg/ml) to extra-high (50mg/ml). There are also solutions available that do not contain any nicotine at all. You should aim to steadily reduce the concentration of the nicotine solution that you use. Start off with a concentrate that works out equal to the number of normal cigarettes that you have been smoking (you can use a free online tool to do this) and then reduce the concentration of the nicotine solution used for the electronic cigarette on a weekly basis. It will depend on how much you are smoking now, but it is not unrealistic to be able to cut out your nicotine addiction within a couple of months.