An electronic cigarette usually consist of three main parts: a battery unit, a vaporization unit (coil) and a clearomizer (tank for e-liquid).
A drip tip (mouthpiece) also exists, usually as part of the tank.
Here the idea is portrayed with a clearomizer (tank), coil and a bottom piece for clearomizer. The coil is screwed into the top of the bottom piece which is screwed into the bottom of the clearomizer (tank). The drip tip sits here permanently mounted on top of the clearomizer. Some tanks also have a replaceable drip tip (mouthpiece).
When refilling e-juice, keep e-cigarette upside down and pour e-juice into the bottom of clearomizer (tank) with coil and bottom piece removed.
Here is pictured one Kanger battery with a button to turn it on. It needs to be pressed and held when vaping and released again when breathing out. Thread is screwed into the base of the tank.
In most cases there is a button to start evaporating and an LED indicator for battery charge status and/or activity. Button on the battery will light up when you hold it, and flash if the battery is depleted.
Some e-cigarettes resemble regular cigarettes and the red LED light is placed at the end of it.
Some finishes are both thicker and longer than regular cigarettes, and contains sufficient reserves for a day's use.
The coil includes one or more heating wires powered by the battery. The battery is always a modern Li-Ion type unit, which is rechargeable.
Electronics in battery unit ensures protection of the accumulator and the heating wire. Some devices can be connected to a computer's USB port, which then delivers energy or can charge the battery.
To charge, unscrew the battery from the tank and turn it into the charger. It can be charged from a wall outlet or an USB plug.
Most vapers tend to have more than one of each part. All parts are consumables with a limited life expectancy: extra battery can be used when the other is empty and must be recharged, additional coil is useful when other becomes burned or soiled, extra tanks can be used to switch between different e-juices easier. Coils do not require cleaning, such as boiling water or cleaning with isopropyl alcohol, they must be replaced.