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?

>>24
I care, therefore you are mistaken.
You're not making any sense.

>>25
The posts you're looking at were made before the sage meme took off[…]
Now that I've seen these posts, you're right.

[…]and were made when the threads they were made in were at the top of the front page anyway.
Moot point, race condition, etc.

Do we really have to be exactly as bad as the worst places on the Web?
That was not an excuse or a justification but rather an explanation I have provided because most upstanding /prog/riders don't seem to be aware of the abysmal state of the outside Internet. (I only discovered it few months ago myself.)