1) Black holes are regions where gravity is so strong that nothing, not even light, can escape and they are formed by the collapse of massive stars at the end of their life cycles.
2) Very massive stars end their lives in huge explosions that blow away the outer parts of the star, leaving behind a very dense core that collapses into a black hole.
3) At the center of a black hole is a singularity, a point where all the dust and gases from the collapsed star swirl around at near light speed due to the extreme gravitational pull.