You're here. You've finally made it. The end. There's nothing stopping you now. Quick, make it to the nearest landmass with any building material you have. The Dragon will come and attack you quickly if you don't.
Use cobblestone or cheap Netherrack to make it to the island. DON'T FALL!
Don't look at the endermen. You have one enemy here. Before you can damage him, you must climb every obsidian pillar and attack the crystal at the top. If you have enough arrows, you can shoot them instead of climbing.
THE DRAGON! Attack him with your bow as he charges you and he'll back off. He really is no threat, however the fight is really long.
The last shot! He'll only be damaged once you take out all the crystals atop the Obsidian Pillars. In this picture, the Pillars are gone, and he's about to eat my arrow.
Loads of experience will rain down. You can build an enchanting table to use all the EXP he drops.
Congratulations! Where the Dragon dies, it'll spawn a portal where you jump into to get back to the world. The signs were added by me ;).