Stars are formed in clouds of gas and dust, known as nebulae. Nuclear reactions at the centre (or core) of stars provides enough energy to make them shine brightly for many years. The exact lifetime of a star depends very much on its size. Very large, massive stars burn their fuel much faster than smaller stars and may only last a few hundred thousand years.
A constellation is a group of stars that can be joined together to form a shape or picture. Many ancient cultures around the world often created stories about the shapes they could see in the night sky.