The End is the third dimension in the game of Minecraft which is accessed by placing 12 Eyes Of Ender around a square of Ender Portal Frames found in a stronghold. Once this is done, the player will be confronted by a flat blanket of stars stretched across the square called an End Portal.
The End is the final dimension in Minecraft. It is supposedly a lost planet or comet, or a piece of another world knocked off by a powerful force. It is populated by Endermen, tall, black, alien-like beings, and the Ender Dragon, a large extraterrestrial being who owns the large rock. The other two dimensions of Minecraft are the Overworld, the main dimension where the player spawns, an infinite world of grasslands, deserts, tundras, oceans, etc, and the Nether, a hellish realm underneath.
The End is covered in large, obsidian pillars with strange entities topping them called Ender Crystals. These crystals give power to the Ender Dragon through strange purple and magenta beams of light, causing the Dragon to gain health/durability. These entities can be destroyed using a bow or other ranged weapon, so that the Dragon cannot heal whilst being attacked. Once destroyed, they will explode, with the same explosion radius as a Charged Creeper.
The Ender Dragon's main and only attack (as of 1.8) is a swoop attack, where the Dragon will lower to the floor of the End, and swoosh by the player whilst trying to bite him/her. This attack will deal about 10 damage to the player in Normal mode, as well as knocking the player backwards in an attempt to throw them off the island. This is a good opportunity for the player to use a sword, axe, or other close-combat weapon to strike it as it comes close. If the Dragon is hit in this way, it will retreat, giving the player time to prepare for the next attack.
Unlike most creatures in Minecraft, the Ender Dragon is damaged by snowballs and eggs, which can be thrown at it from a distance. Players, especially Youtubers/Let's Players have exploited this and used snowballs as an easier alternative to arrows.
Once the dragon is killed, it will explode into a blaze of pinkish lights, accompanied by a strange crackling noise and a small rain of Experience Points. Under the dragon will appear a small, fountain like structure with a tall pillar in the center. Inside the structure will be a "pool" of end portals, and on the pillar will appear a black block called a Dragon Egg. Once the player jumps into this structure/portal, they will be confronted with the ending speech and the credits, after which they will spawn somewhere near their bed in the Overworld.