It's quite simple really:

1. Big hedge fund bet against GameStop stock (shorted up to 140% of the stock, it's called naked short and everybody thought it was illegal since 2008 but that's another story)

2. Lot of small-to-medium investors coordinated over Reddit to take the opposite "bet" en masse (basically buying a lot of GameStop shares) so that the price will go up and "big hedge fund" lose a lot of money.

=> The plan worked. It's a first. Hence the news coverage.

Edit: Typos and formatting