Before you start using the fog command, or any other command in the game, you need to enable commands in your world. If you are creating a new world for it, then you can check the “Enable Cheats” ...

Minecraft cheats and console commands provide a handy shortcut for those who wish to circumvent the resource grind. With the right spawn commands at hand, there's no need to dig deep for gold, iron, ...

The first thing you'll need to do when messing around with Minecraft Java Edition commands is open the title's official launcher. Make sure you have Java Edition selected, and then start the game.