Minecraft is focused on creativity and building, allowing players to build constructions out of textured cubes in a 3D world. Gameplay in its commercial release has two principal modes: Survival, which requires players to acquire resources themselves and maintain their health and hunger; and Creative, where the player has an unlimited supply of resources, the ability to fly, and no health or hunger. A third gameplay mode, named Hardcore, is essentially the same as Survival, but the difficulty is locked on the hardest setting and respawning is disabled, forcing the player to delete his or her world upon death.
A player in Minecraft has a lot of freedom to choose how to play the game, with the primary goals being surviving attacks by monsters, also known in-game as “hostile mobs” (such as Zombies, Skeletons and Creepers) and building shelter. The core gameplay revolves around construction. The game world is essentially made of cubes arranged in a fixed grid pattern which represent different materials, such as dirt, stone, various ores, water, and tree trunks. While the players can move freely across the world, objects and items can only be placed at fixed locations relative to the grid. The player can gather these material blocks and place them elsewhere, thus potentially creating various constructions.

Taken from Wikipedia.