The accretion disk is the orbitting gas and dust that eventually gets swallowed up by the gravity of the black hole. As gases and other particles hit the accretion disk, it sends out x-rays. This is how scientists can find out about black holes, by detecting the x-rays using radio wave telescopes or radio telescopes. Anything passing the event horizon will have no chance getting out of the black hole. If anything hits the singularity, it is immediately destroyed.
Singularities are what is left of the star core.
Black holes also have an immense gravitational force, and even light cannot escape the attraction force of a black hole. There are different kinds of black holes. Three of the main kinds of black holes are the Schwarzschild, Reissner-Nordstrom, and Kerr black holes. Of all of these kinds of black holes, the simplest in composition is the Schwarzchild black hole. It only has a singularity and an event horizon.