A supernova is a cataclysmic explosion, the largest and most violent known to date. These explosions, especially if they occurred somewhat close to us, outshine the brightest stars in their respective galaxies. The process of this
event is not as simple as say dynamite exploding; there are many factors involved. While a star is burning, there is a balance between the nuclear forces and the gravitational forces within the star. While the star is burning hydrogen into helium, all is well. But when the star runs out of hydrogen fuel, it begins to burn helium into heavier elements like carbon and oxygen. Yet these attempts of the star to maintain its equilibrium release little energy and are clear signs that the star is near death. The type of death a
star will encounter is determined by the Chandrasekhar limit.
In other words, a star that is already in its death stages, or a cold star about 1.5 times the mass of the sun, would not be able to support itself under its own gravity. Stars under the Chandrasekhar limit would slowly contract and stop at a final stage of a white dwarf. A star of a mass of about 2 times the mass of the sun would contract until it became a super dense neutron star.

Stars that are greatly above the Chandrasekhar limit would not be able to support themselves when the last of their hydrogen fuel ran out. These stars burn up their hydrogen fuel into helium very quickly; say within 100 million years, as opposed to our sun whose life span is about 9 billion years. These stars would end their lives in the form of a mammoth explosion unlike any other. They would begin to contract indefinitely until they reached a point of infinite density and infinitely small size, a singularity. The gravitational force would be so strong that not even light would be able to escape. This is the birth of a black hole.
The heavier elements produced by the star in its last
stages of life, as said, do not provide enough pressure within the star to counterbalance its gravity. So as this explosion occurs, all of these heavier elements are flung out into the universe and provide the building blocks for new generations of stars and planets. This supernova system can be thought of as a recycling method in which a star uses up matter to form energy, and then gives some of it away during death.