The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and glows red. The star has now reached the red giant phase. It is red because it is cooler than it was in the main sequence star stage and it is a giant because the outer shell has expanded outward. In the core of the red giant, helium fuses into carbon.
All stars evolve the same way up to the red giant phase.
The amount of mass a star has determines which of the following life cycle paths it will take from there. As the core collapses, the outer layers of the star are expelled. A planetary nebula is formed by the outer layers. The core reamins as a white dwarf and eventually cools to become a black dwarf . However, their life cycles start to differ after the red giant phase.