Black holes is an object that has high gravitational force that not even light can escape. It is formed when a massive star die and collapse, just like neutron stars form from a supernova explosion. The black hole is star could not do anything to stop the gravitational collapse. The star core was crushed by the collapse.
The black hole is shield from the outside world called the Event Horizon. The sphere the black hole is where light could not escape. Anything that crossed the Event Horizon is gone forever. Many astronomers believe that most of the galaxies has many black holes in their core. The black may have taken in the mass of billion stars.
If you enter the black hole, the gravitation force will rip you apart but even though you survived, and crossed the horizon, there is no turning back. The best is to avoid the black hole at all cost. If you were to cross into the black hole, the people on Earth will never seen you crossing the Event Horizon on Earth. You will appear to be in slow motion and then frozen in time. If you are to change your mind and return back to Earth, you find that Earth is in the future.