It is a subscription system that gives access to be able to play online on Playstation 4 and/or Playstation 5 consoles.
The service gives access to 2 games that can be downloaded for free per month and playable as long as you pay for the subscription. Members also have access to some bonuses and discounts.
You must access this service to save game backups to Playstation’s servers. When they are saved at Playstation, it makes it easier to share them between consoles, and it allows you not to lose your progress in case of breakage or loss of the console.