3 modes to choose. In creative mode you can build anything you want, even set up PVP maps that can produce scores, use a command block or input commands in the chat bar. Put people in adventure mode and then play in the maps you create. In survival mode you do just that, survive in a world full of digital nature, and turn that nature into your world, build a house for protection, farm land for food, create automatic gardens, build railroads to get around your world, lastly find the items needed to get to the Ender Dragon to win the game. Minecraft is 7 times the size of earth so good luck finding that end portal :D I did, after exploring for about 7 months in my world. Oh and the worlds you start are always different not one will be the same, because the game seeds itself it creates itself with variables rather than set values, why this game is so bad ass, it is like real life, unlimited without glitch.