Galaxies consist of millions of stars, gas and dust particles that come in three main forms - spiral, elliptical, and irregular galaxies. The document discusses the different types of galaxies like the Andromeda and Milky Way spirals as well as the Ursa Major elliptical galaxy. It also provides information about our Milky Way galaxy, noting that it is a medium-large spiral galaxy with around 200 billion stars and that our solar system is located on the edge of one of its spiral arms.