During the main sequence stage, the Sun's energy output and temperature remain relatively stable. The Sun gradually fuses hydrogen into helium in its core, and as it does so, its core becomes hotter and denser. The Sun's surface temperature also increases slightly over time.
At the end of the main sequence stage, the Sun will run out of hydrogen fuel in its core. This will cause the Sun to evolve into a red giant star, which is a much larger and cooler star. The Sun will then eventually collapse under its own gravity and become a white dwarf star, which is a very hot but dense star.
