Constellations are fixed patterns of stars.
Observers have always recognized patterns among the thousands of stars visible on a clear night. Constellations are fixed patterns of stars.
For example, the stars of the Orion constellation can be thought of as tracing the outline of a hunter with a shield, an upraised arm holding a club, and a sword hanging by his belt.
The shape of Orion and other constellations stay the same throughout the night, even as the stars as a group move slowly across the sky. This site has an animation called The Celestial Sphere that shows the constellations rising and setting over the course of a day.