How do stars generate their light and heat energy?

Stars generate light and heat energy through the process of nuclear fusion, primarily converting hydrogen into helium in their cores. This fusion releases a tremendous amount of energy in the form of light and heat, which radiates outward. The immense gravitational pressure in a star's core facilitates these reactions, maintaining the balance between gravitational collapse and the outward pressure from fusion energy. This process is fundamental to a star's lifecycle and determines its brightness and temperature.