Black holes are what happens when the escape velocity of an object (in most cases, a star) exceeds the speed of light. Or, what happens if you divide by zero.
To understand a black hole, you must first understand the idea of escape velocity. Escape velocity is the speed an object would have to travel in order to escape a source of gravity. For example, Earth's escape velocity is 11.2 km/s, or 20, 053.6865 mph. You would need to be traveling that fast in order to clear the Earth's gravitational pull and get into space.
Like these guys, godspeed you beautiful bastards.
However, when it comes to a black hole, the escape velocity is greater than the speed of light, which means that it has a tendency to drag everything that comes near it towards it center. The only way to escape a black hole would be to travel faster than the speed of light, and that is incredibly impossible, as it would do silly things like make your mass infinite.
At least we think that's what this equation means.
So it's best to just stay away from them.
First of all, it will happen just like this.
Well, no one actually knows what will happen to you, but plenty of scientists have used the power of science to come to a common conclusion. So, it'll go a little something like this, depending on the size of the black hole.
With a small black hole, you are merely ripped apart on the molecular level all while being stretched out into a long, thin shape towards the center of the hole, where you will then be crushed. Scientists have named this particular stretching phenomenon "spaghettification".
Now, with a bigger black hole (it would have to be pretty gigantic) the gravitational pull would be a little weaker, which means that you most likely wouldn't be ripped apart until after you pass the event horizon (which is a boundary in black holes beyond which events cannot affect an outside observer, or something). In that case as you are pulled and spaghettified, it will look like you are surrounded by a huge, distorted, one way mirror, where you can see everyone but they can't see you. As you grow closer to the final embrace of a merciful death, the image will grow more and more distorted. Until well...you are ripped apart on the molecular level.
We'd like to think it'll be just like the Soundgarden video.
So what're the odds that any of this will ever happen to us? Well, if you buy into all that Large Hadron Collider business, it's incredibly likely.
But it's cool, it will all happen so quickly you will barely realize it.