Vaporizers are meant to heat dry herbs or extracts to the point of vaporization, but not to the point of burning. This happens by controlling the internal temperature of the heating chamber electronically, allowing you to vape in peace without worrying about the carcinogens that go along with combustion.
Conduction & Convection - Vaporizers normally use one of two main heating systems: convection or conduction.
Conduction vaporizers heat substances directly using a conductive substance like metal, steel or ceramic. When handling these types of devices, the substance normally sits atop of the heating element, and the heat is administered like a pot or frying pan on a stove. Without stirring, the heat transfers only to the substance that it is touching, so this may lead to some uneven heating. Some herbal vaporizers, and the majority of extract vaporizers, use this heating method.
Convection vaporizers heat substances indirectly using heated forced air that passes through the chamber to heat the herb to the point of vaporization. Convection vaporizers often provide the evenest heating and don't require stirring, as the heat is transferred uniformly throughout all the substances.