This sequence of drawings shows what will happen to a star like our sun over its lifetime. To learn more about this stellar aging process, visit The Life of Sun-like Stars.
Our Sun is typical low-mass star in the galaxy, in the prime of its life, steadily fusing hydrogen into helium, as it will do for another five billion years. For an overview of a star's adult life, check out Main Sequence Stars.
You have probably heard that the Sun will one day expand and consume Earth. In fact, the Sun might even expand to the orbit of Mars. Read about how this will happen here.