The ancient Greeks saw many other constellations that we still use today, including Aquilla the Eagle, Leo the Lion, and Corona the Crown.
When Europeans began exploring the Southern hemisphere, they saw completely different stars, which formed completely new patterns. They began naming Southern hemisphere constellations. They called one Crux, the Southern Cross and another one Centaurus, the Centaur. They even named one constellation Microscopium, the microscope!
Astronomers today recognize 88 constellations, spread through the sky over the two hemispheres. When astronomers identify a point in the sky, they often do so by naming the constellation that the point is closest to. For example, the large spiral galaxy M31 is near the constellation Andromeda, so astronomers sometimes call it the Andromeda Galaxy.