The atomizer is the "heart" and one of the major components of the electronic cigarette. It is the device which converts the e-liquid of your choice in vape. This is achieved by a resistor which is heated and evaporates the e-liquid.
Each atomizer depending on type, yields differently the flavor you choose. You can find "clearomizers" who have high resistance and oozing hotter steam while for example the Bottom Coil Cartomizers have lower resistance resulting vape have to travel a greater distance and so it comes out colder .
The atomizer coils are expendable and have a lifespan of 10 to 30 days. This depends on the manner and the frequency that you use them.They must be replaced for hygienic reasons but also because their performance deteriorates with time.