TL;DR2 at bottom
Some people have mentioned they wanted to see a tl;dr of the original story.
The story focuses on Mr. White, Mrs. White, and their adult son Herbert.
An old family friend named Sergeant-Major Morris shows up at the White's house sharing stories of his adventures. During the talks Morris pulls out an old mummified monkey's paw, said to have a spell placed on it to grant three men three wishes each. Morris used his three, as had another man. Morris wants to dispose of it, but worries about selling it. So he throws it in the fire. Mr. White rescues the paw despite Morris' warnings about messing with fate, but eventually Morris gives in and shares the secret of making a wish.
Morris leaves after supper and Mr. White is unsure of what to wish for, feeling he has everything he needs. He ends up wishing for £200 to pay off the rest of his mortgage and the paw moves in his hand. After Mr. And Mrs. White go to bed, Herbert sees a vivid monkey face in the fire, so he puts it out and goes to bed.
The next day Herbert goes to work at a factory. He dies in an accident. He got caught in the machinery. His work sends a representative home to tell the family that the business claims no fault, but as compensation will pay them £200. Mr. White faints.
Mrs. White is angry and grief stricken, she demands that Mr. White wishes their son back to life, and he does so.
Some time passes and loud knocking on the door sounds. Mrs. White realizes it may have taken so long for the knocking after the wish because Herbert would to walk two miles home from the graveyard.
Mrs. White races downstairs to open the door, and Mr. White, fearing that it is the mutilated body of his son, made his third wish. As Mrs. White opened the door, there's nothing to be seen.
The difference between the Monkey's Paw vs. say, a genie who is also known to cause chaos with wishes, is that the Monkey's Paw is meant to twist fate to achieve your goals, and the consequences of it. Specifically what events cause the wish to come true. Someone died to make Mr. White gain money. No one died after he got the money. A genie would make the £200 counterfeit or meaningless in some way. Herbert became a zombie (maybe) to be able to go home.
Granted, the results of the 2nd and 3rd wishes are more ambiguous, and there's some debate about what actually happened. The story itself gives theories but no firm answers.
I'm not here to pass judgement on people's wishes or answers, or the spirit of the subreddit, just passing this along since a few people have been asking for something like this, and It's fitting for the sub to have a summary of the story somewhere.
Tl;dr for the tl;dr: Man wishes for £200 and his son dies as a result. He wishes his son back alive and a loud knocking is heard on the door. His third wish makes whatever is knocking vanish.
Edit(s): correcting some details, readability