The ability to play games has not yet been released. At the moment, you can try out some templates and previews in the Game Maker software.
There are some free-to-play (F2P) games in The Sandbox. There will also be some non-free games in The Sandbox. Whether a game is free-to-play or not is entirely up to the designer of that game.
Yes, you can potentially earn $SAND through Play2Earn mechanics. You can then use this $SAND to purchase ASSETs, avatar customisations or to access and play non-free games, amongst other things.
Some blocks or ASSETs can be configured by the game designer to be destructible.