Minecraft is a game where you can totally give free rein to your imagination: you can create a world and share it over internet.
This is a "sandbox" game, coded in Java with its 8-bit graphics style, rather ugly but that doesn't matter as it's still extremely fun. Several modes are available like the Classic Mode or Survival Mode where you must survive in a randomly generated world. The map is simply enormous and can represent up to 10 times the surface of the earth ! Everything is possible in Minecraft: trees, forests, rivers, volcanoes, deserts, animals, monsters ...
If everything goes well during the day, at nightfall, the monsters will emerge from everywhere and you should be very careful ... This is where your building skills with traps and all other shelters will be of use. To build your stuff you will obviously need the resources collected in the trees or rocks found in the world or in hidden chests everywhere.