This is an example of a Hertzsprung-Russell diagram; a plot of luminosity <i>versus</i> spectral class for a group of stars. The diagonal band labelled "main sequence" is where dwarf stars such as the Sun spend most of their active lifespan. Red giants and supergiants are evolved stars with a mass greater than a red dwarf, that are burning elements heavier than hydrogen. However, White Dwarfs are quite dense, non-luminous, but are still less in mass than supergiants.  Once this supply of fuel is exhausted, these stars will migrate to the lower left on this diagram, becoming white dwarfs.
Illustraion by R.J. Hall
CC BY 2.5
This illustration by the contributor is based on Figure 3 (p. 52) of <i>Great Ideas and Theories of Modern Cosmology</i> by Jagjit Singh.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[1]</a></sup>