Theory:

Constellations are a group of stars with a recognisable shape. These shapes resemble the familiar objects known to the people to recognise them easily.
The shape of the constellation does not change and appears to move from east to west. There are totally \(88\) officially known constellations in the universe.
 
orion hunter.png
A constellation
 
A constellation has a large number of stars, out of which only bright stars can be viewed with our naked eyes. The stars are not equally spaced, but they seems to be aligned in the same line of sight in the sky.
Types of constellations:
There are different types of constellations present in the sky. They are
  1. Ursa Major
  2. Cassiopeia
  3. Orion
  4. Leo Major
four constellations.png
Types of constellations
 
To identify the constellations in the night sky, one should know where to look for it.
Reference:
https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Orion_%28constellation%29_Art.png/624px-Orion_%28constellation%29_Art.png
https://static.thenounproject.com/png/370457-200.png