This is how I understand it.
Basically lots of hedge fund types placed a "Short", a bet that Gamestop shares would drop in the near future. Effecivly they bought shares undervalued in the expectation the shares would drop even lower than this value and they would be able to profit off the difference.
Redditors knew this and started purposely buying the stock to inflate it away from this predicted drop. If the shares are way above this predicted drop those who predicted it have to pay out the difference.
Makes sense to me, no idea if that helped anyone.
You don't buy shares when you short.
You borrow them, and sell them, with the expectation that you will be able to buy them back cheaper, return the stock to the lender, and pocket the difference.
Depending on the mechanism they shorted/borrowed with, they may be on a fixed term contract. So once that date comes around, they must buy and return the stock. That expiry date for much of the GME shorts is Friday, hence WSB are trying to keep the price pumped until then, forcing the hedge fund shorts to eat a massive loss.
Of course, at some point, all these WSB people sitting on their paper profits are going to try and cash in and liquidate their positions.....and GME is going to go through the floor.
We're still very much in an extended period where anyone buying stock is seeing easy, large profits. Might well trigger a sell off in the rest of the markets tbh.