The changing of the constellation from season to season is due to our planet's rotation around the Sun. When we circle the Sun, different part of the sky move into and out of its glare. For example, the constellation Orion dominates the evening sky in January, but Leo replaces him by March. By June evenings, Leo is then replaced by Scorpius. From the demonstration of a star chart, you will see the changing of the constellation for different seasons.
Astronomers use star charts to locate stars and other objects.
Star charts are much like the maps of the Earth. In the star Charts, declination and right ascension are replaced for latitude and longitude. Knowing the lines of declination and right ascension, astronomers locate the position of stars on the celestial spheres. Eventually all the stars are so far away that it is impossible to measure the distance in miles or kilometer. However, astronomers measure the distance in terms of how long it takes their light to reach us.