How to screw over short-sellers for fun and profit

A coalition of people on the Reddit forum WallStreetBets, brought the US financial system to its knees. Specifically, they took a random failing company, GameStop, artificially made it one of the most valuable companies on earth, and utterly screwed over a bunch of short-sellers. But what is short-selling, what is a short squeeze, and why is a random Reddit forum being hailed as the greatest financial geniuses of our time? Buckle up for the most easy-to-understand explanation of Gamestonk on the entire internet. #shouldbebetter #esbb