A stars expands as it grows old. As the core runs out of hydrogen and then helium, the core contacts and the outer layers expand, cool, and become less bright; this is a red giant.
After expanding and reaching the enormous red giant phase, the outer layers of the star continue to expand. As this happens, the core contracts; the helium atoms in the core fuse together, forming carbon atoms and releasing energy. The core is now stable since the carbon atoms are not further compressible.
Now the outer layers of the star start to drift off into space, forming a planetary nebula (a planetary nebula has nothing to do with planets).
The star loses most of its mass to the nebula. The star cools and shrinks; it will eventually be only a few thousand miles in diameter!
The star is now a white dwarf, a stable star with no nuclear fuel. It radiates its left-over heat for billions of years.
When its heat is all dispersed, it will be a cold, dark black dwarf - essentially a dead star (perhaps replete with diamonds, highly compressed carbon).
A nova is a white dwarf star that suddenly increases in brightness by several magnitudes. It fades very slowly.