What is the 2 stage of the red giant?

The second stage of a red giant occurs after the core has contracted and heated up sufficiently to ignite helium fusion. This stage follows the initial hydrogen burning phase, where the star expands and cools, giving it a red hue. During this phase, helium in the core fuses into carbon and oxygen, while the outer layers continue to expand and cool. This process leads to the star becoming larger and more luminous before it eventually sheds its outer layers, forming a planetary nebula.