Black holes are, simply put, HOLES in space-time (more about that here: The fabric of the universe itself) with gravity so strong that not even light can escape from it (thus making it black). When you start getting close to a black hole, the pull of gravity is stronger on the closer part of your body to the black hole, and it will stretch you (or any object that comes too close) apart.  It’s called spaghettification.  Watch this for more info:

https://www.youtube.com/watch?v=6H6CcbIMH7I

That video explains a lot.  Let me explain some of the most important parts of a black hole, since this section isn’t just about what would happen if you fell into a black hole, it’s what black holes are (though falling into a black hole is an important thing about it, at least for us humans).  The event horizon is the point of no return, not even light (which goes about 186,000 miles a SECOND) can escape.  The singularity at the center is so dense that– well, we don’t even know how dense it is.  Let’s just say it’s SUPER dense.  And lastly, a quasar is when a black hole shoots out remnants of things it tried to eat but was too full– in essence, it threw up.

<– That’s an artist’s rendition of a quasar