The term “BLACK HOLES” first use by in print media by a science journalist ” Ann Ewing” in her science article “‘Block Holes’ in Space”, dated 18 january 1964. Generally  Black holes are the places of mystery, Presently Physics agree with the existence but thier is no theory which explain, What happens inside a black holes ? But If we understand the theory of relativity which given by Albert Einstein, Published in 1915. Then we can understand the black holes.How can we observed a black holes ?Black holes cannot be observed directly on account of both their small size and the fact that they emit no light. They can be “observed,” however, by the effects of their enormous gravitational fields on nearby matter.Black Holes:Black Holes is a region in space which consist a strong gravitational, Strong gravitationl force means where nothing can escaps from inside it, like: particles and electromagnetic radiation, means of electromagnetic radiation is “light”. In simple word,”A Black Holes completly behave like an ideal black body which absorb every ray light(mean color). A black hole has only three independent physical properties: mass, charge, and angular momentum.The theory of relativity suggest that black holes can be formed by the large weight star’s death, In other word when a star has exhausted, Its internal thermonuclear fuel ( Known as Nuclear Fusion) comes to end at their core and at outer boundery fusion is continue because gaint size of star the core becomes unstable and gravitationally collapses inward upon and the stars outer layers are blown away. The crushing weight of constituent matter falling in from all sides compresses the dying star and this is the reason of higher gravity forces, A black holes mainly consists two main terms. They are Event Horizon also knows as Schwarzschild Radius.Gravitational Singularity Or Spacetime Singularity.Event Horizon:Event Horizon is a term which refer a distance where events cannot afftect an outside observer, means a “point of no return”, where gravitational force can not pass anything, so a observer at the outside can not see block holes because only those thing which refelect the light.We can say that An event horizon is most commonly associated with black holes. Light emitted from inside the event horizon can never reach the outside observer. One of the best-known examples of an event horizon derives from general relativity’s description of a black hole, a celestial object so massive that no nearby matter or radiation can escape its gravitational field.Gravitational Singularity:Gravitational singularities are mainly considered within general relativity, where density apparently becomes infinite at the center of a black hole.The crushing weight of constituent matter falling in from all sides compresses the dying star to a point of zero volume and infinite density called the singularity.How can we know a star become a black holes:How can we know a star become a black holes ?An Indian Scientist Chandrasekhar observed when a star has exhausted which weight is less than 1.44 times of Our sun become A dwarf star but when a star has exhausted which weight is more than 1.44 times of our sun become A BLACK HOLES. This theory is known as Chandrasekhar limit.In short, “The Chandrasekhar Limit is now accepted to be approximately 1.4 times the mass of the sun; any white dwarf with less than this mass will stay a white dwarf forever, while a star that exceeds this mass is destined to end its life in that most violent of explosions: a supernova.”