All you have are the 9 blocks below you to start your world. Every time you break a block, all 9 will refresh into something completely random. It can turn into any block in the game and it can sometimes be a chest that can contain any non-block item in the game! Make your way to the naturally generated end portal to beat the game!
You may have to do a little prep to get your world ready. Make sure that there are barrier blocks below the 9 blocks so that sand doesn't fall and constantly refresh the blocks (unless you want that, do whatever you want of course). That should be it! Empty your inventory, go to survival with /gamemode survival, and enjoy the world!
You may do whatever you want with the 9Block datapack in the saves file.
