a paralax can be used to measure the relation of the distance between one star to another.such as, when you take a picture of a star, and another of that same star six months later, with the paralax...
It is used to determine the distance between objects such as celestial bodies. Example: the distance of stars from the earth can be measured by using the parallax.
The star's apparent position in the sky changes, due to Earth's movement around the Sun. Earth's orbit has a diameter of 300 million kilometers, so Earth has this much change in position each year....
Well it's pretty simple, you know what a parallax is, as you experience it all the time. Like your in the car, and your moving... you can see the stationary objects closer to you seem to be moving...