From this we learn that the spiral arms are regions of active star formation, while the bulges are mostly older stars. In spirals, there is an overall rotation that causes the galaxy to collapse into a disk. But this is not the case with many galaxies that instead have a spherical or football shape, and are called ellipticals. Ellipticals contain predominantly old yellow stars, and there is little active star formation going on in them. The number of stars in elliptical galaxies has a wide range, from a million in the dwarfs up to trillions of stars in the giants.
Spirals tend to have less of a range, with typically one to a hundred billion stars.
Examples are the Small and Large Magellanic clouds, that are satellite galaxies of the Milky Way easily visible from the Southern Hemisphere. Irregulars have distorted shapes and lots of star formation because they are being tidally disrupted - for example the SMC and LMC are being torn apart in places and compressed in others by the tidal effects of our Milky Way galaxy. Billions of years from now, they will have been completely shredded. Galaxies are usually not found on their own. They are usually found in groups or clusters, that even are grouped together to form large superclusters in space.