Explore the fascinating world of astrophysics in this comprehensive lecture on diffuse stars, part of a series on neutron stars and black holes. Delve into the nature of stars, their formation, and internal processes as explained by renowned physicist G Srinivasan. Learn about Eddington's theory of stars, gravitational pressure, hydrostatic equilibrium, and the mass-luminosity relation. Discover why stars have specific masses and compositions, and understand the nuclear reactions that power them. Investigate concepts like quantum tunneling, fusion reactions, and the proton-proton cycle. Gain insights into the Sun's energy production, lifetime, and core composition. This lecture provides a solid foundation for understanding stellar physics and sets the stage for exploring more advanced topics in astrophysics.