> What I think a black hole is is a point. No length, width, or hight.I 
> am not too sure though of how it keeps a gravitational field.

A black hole is nothing more than a collection of matter. Granted it's a 
very large collection of matter taking up a very small space, but it's 
still just matter (well, and energy, but matter and energy are the same 
thing, right? E=mc^2 and all...)

Think of it this way. All matter curves space, right? Well, because it's 
so hard to visualize this curvature (because space occupies the accursed 
3rd dimension with width, height, and depth) scientists have come up with 
an easy way to think about it.

Imagine space as being only 2 dimensional.... like a piece of paper or a 
sheet of plastic. (Forget that it is 3 dimensional and just think of it 
as 2.) Then, with nothing in it, the space would be flat, like this:

_________________

When something is present in this space (like a planet, star, bowling 
ball, or even just ordinary energy) this flat surface becomes curved 
(imagine taking a basketball and placing it in the middle of a sheet of 
plastic... it would cause the plastic to bow down under it's weight) like 
this:

------\_/--------

Okay, now imagine taking a very large object (like a bowling ball in the 
plastic example) and compressing it to take up a very small space (like, 
say, the tip of a needle in the plastic example.) So now you have 
something that is very heavy, yet very small. What happens to this flat 
surface is exactly what you'd expect under this circumstance, it rips:

--------. .------

This technique of visualization is called an "embedded diagram" and my 
first black hole simulation that I ever did was of an embedded diagram 
of a black hole. The pictures from this can be found on my image library 2 page,

http://www.physics.arizona.edu/~hart/bh/bhimage2.html

Plus, the main logo for my Black Hole Simulations page has one as well.

It's important not to think of this diagram as the way a black hole 
REALLY looks. It's merely a way of being able to see what the hole's 
effects are upon the space it's in.