If the Big Bang was a tremendous release of concentrated energy, then temperatures must have been so high that atoms would not have existed. The universe would have consisted of radiation and elementary particles, which would have spread out over a large volume. These radiation particles make up the static which Wilson and Penzias discovered in 1964. Stars are believed to begin life as collapsing masses of hydrogen gas called protostars. As they contract, their temperatures rise, until they reach a point where nuclear fusion begins.
Energy is released, and the star stabizes as a main-sequence star, which is the normal type of star.
The brightness of stars comes from this released energy, which is a result of the thermonuclear reactions. After billions of years, the hydrogen is used up, the core contracts, and gets even hotter. Meanwhile, the envelope expands and cools, and the star becomes a red giant. At this point, smaller stars cool further, becoming white dwarfs, growing dimmer, until they finally fade out entirely. Heavier stars, however, contract further due to their greater gravity, until the pressure becomes so huge that protons and electrons combine to form neutrons, and the star becomes a huge nucleus of neutrons, or a neutron star.