According to the Harvard-Smithsonian Center for Astrophysics "Supernovae are exploding stars. These stellar explosions are responsible for creating all the elements heavier than iron and for distributing the elements synthesized throughout the star's lifetime to the interstellar medium. 

Supernovae come in two distinct physical flavors. Type Ia supernovae result from a thermonuclear runaway in a carbon and oxygen White Dwarf star that reaches a critical mass of 1.4 solar masses. With a peak luminosity of 9 billion times that of the Sun, Type Ia supernovae can be seen out to a sizeable fraction of the visible Universe, and hence serve as distance indicators on cosmological scales"

The objective is  "To find distances in space, astronomers use objects called "standard candles." Standard candles are objects that give a certain, known amount of light. Because astronomers know how bright these objects truly are, they can measure their distance from us by analyzing how dim they appear." (hubblesite.org)

To sully being to understand the typa Ia supernovae one must also understand the White Dwarf.... More on that latter