Monads. How do they work?

I'm reading "Learn you a haskell for great good." I've gotten through most of it but I want to learn about Monads.

What the fuck are they?
What is their purpose?
How do they work?

>>23
The posts you're looking at were made before the sage meme took off, and were made when the threads they were made in were at the top of the front page anyway. I remember them.
All of his recent posts have been saged, and all of his anonymous ones are too.

If I have time later on I'll do a graph showing how sage use on /prog/ evolved over time. It's been a while since we had a history graph.

Have you seen the rest of the Internet? I recommend a look at GameFAQs.
Do we really have to be exactly as bad as the worst places on the Web?