Minecraft is a game based on your imagination. In minecraft you can build anything you want.
The game is really simple, there is 2 types of game mode in minecraft PE, creative and survival.
In creative you will have unlimited resource and you can fly. To open inventory just tap the box with three dots and chose the block you want. You place the blocks by tapping it on the ground.
In survival you have to collect your own resources. You can destroy the blocks by press-hold the block and then moving foward to collect it. To place the block it is also the same as the creative ones
To craft, you go to the inventory and tap the bookshelf and pick the items you want to craft and click craft. There are nights also at survival, at night zombies and other creatures will spawn and they can harm you if you get close to them. You can kill them by tapping them until they die.
  Thats all you need to know for the basics, so good luck playing it :)