The tremendous amount of mass in a black hole condensed at a single point known as Singularity, creates a gravitational hole, that bends space to the degree that nothing can escape, not even light.
At the local science center there is a display that illustrates a black hole well. The display has a ramp where a coin can be launched. The display is an inverted cone. The diameter of the inverted cone gets smaller as the angle of the cone increases. The coin falls down into the cone, moving faster and faster until at the very bottom the coin disappears into a small hole.
A black hole is much like the display, The gravitational hole does not allow anything to escape. Any object (including light) that crosses the line of singularity will fall into the gravitational well. Object coming near the black hole will have their trajectory changed bending them toward the black hole.
It was this bending of light due to the change in time created by the gravity if the sun that verified Einstein's theory of relativity. At the boundary of the singularity time stops and ceases to exist. Any object that enters a black hole will never escape.