The stars are not fixed but they are just constantly moving. We see them in the same position every night because they seem to be very small to us and also due to the earth's revolution.
If you factor out the daily motion of the stars across the sky due to the earth's rotation, you end up with a pattern of stars that seems to never change. The stars seem so fixed that ancient sky-gazers mentally connected the stars into figures called constellations that we can still make out today. But in reality, the stars are constantly moving every time. They are just so far away that the eye without any instrument cannot see their movement. But sensitive instruments can detect their movement.