The power button still turns the console on and off, but the Reset and Open buttons have new functionality.
The Reset button acts as a way to suspend games, enabling players to pause a game anywhere and come back to it later without having to use memory cards or requiring the game to have its own save system.
Similarly, the Open button is used to swap out games. Instead of opening a CD-ROM reader — like the original PlayStation console — you'll push Open to "swap virtual discs." Sony has yet to show what the console's user interface looks like, so it's not clear exactly how this will work.
On Nintendo's NES Classic Edition and Super NES Classic Edition consoles — miniature versions of classic game systems — you're able to save four "suspend points" for each game. It's likely that Sony will adopt a similar system.