What is a black hole?how can something have infinite density and time freezed?

k buddy i'll my best to explain this...
you know there are a lot of stars in the universe.. these stars are classified according to their existence.... when a star is too old..there would be some reaction going on in the star.. this results in the explosion of the star.. this explosions sometimes creates a black hole.. this black hole is an area of very high gravitational field.. so what ever passes through its path.. gets absorbed by it.. it is said that even light cannot escape a black hole..

To add to the above: These old stars collapse in upon themselves. Their gravity and density are still there so stronger that nothing can escape, not even light or radiation which is why we can't see it, but we can see the affect it has on objects around them.
Time doesn't freeze in or around a black hole, it slows down significantly.
Space and Time are intricately linked together, so much so that Einstein coined the word: spacetime. To be used as one word, one concept. So when that area of space is being warped by the black hole's gravity, so is time.