You can buy and install Minecraft on both iPhone and Android. If you already have Minecraft installed, skip this step. Tap the Minecraft app icon, which resembles a block of dirt. It's at the top of the screen. You'll find this option near the top of the screen. This option is near the top of the screen. Doing so will open the world's creation page. If you don't see this option, first tap the New World tab in the upper-left corner of the screen. Type in the name that you want to use for your world. The default name is "My World". Tap the "Difficulty" drop-down box, then tap a difficulty level in the drop-down menu. On higher difficulty settings, monsters do more damage and are harder to kill. Scroll down through the "Game Settings" section of the screen and review the game options. You can change any of these before launching your game, though some options may not be available after you start the game. It's on the left side of the screen. Doing so will confirm your game settings and create your world. Once the world loads, you can begin playing Minecraft.

Summary:
Buy and install Minecraft. Open Minecraft. Tap Play. Tap Create New. Tap Create New World. Enter a name for your world. Select a difficulty. Adjust other world options. Tap Create.