The very first thing to learn electronics is to understand the two different kinds of materials:
Due to the atomic structure of materials or elements, conductors have a lots of carriers which are electrons and insulators have none and therefore they do not conduct electricity. Refer to the switch to see how a switch is designed to control when the circuit is on, that is, conducts, or off, that is, do not conduct. Air, by its nature, is not conductive. However, if the electrons have enough energy or in other words, the voltage is high enough, air does allow electrons to flow and that is why lightning does happened because high energy electrons impact on air or water molecules in air and kick other electrons out of their core shells of the molecules to get free and keep colliding with other air molecules or water molecules in the air.
Experiments had been done to evaluate the breakdown voltages of some insulating materials. Namely the breakdown voltage for air is 30 kV/cm, the breakdown voltage for porcelain is 70 kV/cm,the breakdown voltage for rubber is 270 kV/cm,the breakdown voltage for glass is 1200 kV/cm, and the breakdown voltage for mica is 2000 kV/cm,