What is the red giant?
The red giant star has a mass like out sun. The red giant is the last phase of a stars life.
How is it formed?
The red giant forms from a main sequence star; hydrogen reduces as hydrogen atoms fuse together. Since the helium atoms are heavier than hydrogen atoms they sink to the center of the core; the hydrogen atoms burn in the shell around the helium in the center. The hydrogen fusion reactions become less efficient in the core, the gravitational collapses in the core, because of this the luminosity of the star expands and the outer layers cools and the red giant are born.
What goes on inside?
Inside the shell of the Red Giant the core begins to shrink and luckily it heats up enough to fuse the helium nuclei together into heavier ones. Heavier nuclei are produced inside the core of the red giant, at the center are iron nuclei.