Here's a breakdown of the stages:

1. Protostar: This is the initial stage, where a cloud of gas and dust collapses under its own gravity.

2. Main Sequence: This is the longest stage of a star's life. During this stage, the star fuses hydrogen into helium in its core, releasing energy that makes it shine. The star remains in this stage for millions, billions, or even trillions of years, depending on its mass.

3. Red Giant or Supergiant: When a star runs out of hydrogen fuel in its core, it starts fusing helium into heavier elements. This causes the star to expand significantly, becoming a red giant (for smaller stars) or a supergiant (for larger stars).

4. Later Stages: The later stages vary depending on the star's mass. Smaller stars will eventually become white dwarfs. Larger stars might go through multiple stages, becoming a supernova, neutron star, or even a black hole.

So, while "the third stage" is technically the Main Sequence, it's important to remember that a star's life is much more complex and has multiple stages depending on its mass and evolution.