1) Our Sun is about 5 billion years old, and lies on the Main Sequence.
2) In 5 billion years, its core will have burned
90% of its Hydrogen and the Sun will leave the Main Sequence.
3) The Sun's core will collapse and heat up,
simultaneously pushing out the outer solar
envelope.
From the outside, the Sun will have grown
first physically larger AND then also cooler.
4) The Sun will burn as a Red Giant for about
1 Billion years..
5) Until it is able to ignite
Helium burning in its core.
6) However, the core continues to collapse and heat up, puffing
out the Sun's outer atmosphere even larger, entering the second
red giant stage.
7) With time, the Sun's out atmosphere, now extremely extended and
tenuous, will expand away as a Planetary Nebula.
8) Sooner or later, the hot central core is exposed. This hot core is
what we see as a White Dwarf.
9) White Dwarfs do not evolve, they simply slowly cool off, as they radiate their energy away.