Stellar Classification

Human physicists and astronomers use a traditional system for classifying types of stars which goes back to the times before Emergence.
This usually consists of a letter denoting the primary type of the spectrum of the star with a following number representing the subtype. For example Earth's sun, Sol, is a G2 star.
In brief and simple terms, smaller low mass stars tend to be more common, cooler, fainter and red and are often called "red dwalf" stars. These are mostly class M stars. As mass increases, luminosity increases and colour moves up the spectrum from red to blue. Classifications K, G and F consist of orange through to yellow. This is considered to be a sweet spot for hosting life. Stars like this are long lived enough for evolution to have time to bring forth complexity, whilst also being generally more stable with wide habitable zones for planets. Most of the populated worlds within the Bubble are part of stellar systems with stars of these types. Beyond that, we move to more massive white and blue stars that fuse at higher temperatures and burn their fuel more quickly. The hotter and brighter a star, the shorter lived it is. Classes A, O and W lie at this end of the spectrum and the most massive ones will end their lives in a catastrophic explosion known as a supernova.
There are a number of exceptions to the simple pattern described above, most notably for the so called "red giant" stars which are large, diffuse and cool. These are a late stage development in the life cycle of some massive stars.
For a more comprehensive technical explanation refer to the following external article which describes the full system of stellar classifications.