How can I kill the enderdragon in minecraft?

Destroy all the crystals which are on top of the obsidian pillars. Some are in cages so you'll have to go up there and remove them. Be careful because they explode and will most likely kill you or knock you off.

Once they're all destroyed, you can start killing the dragon. The dragon uses the crystals to heal so you can't really kill it without destroying the crystals.

Use a bow to shoot the dragon in the air, every now and then he will come down to the portal and hover above it. That's where you go in with your sword as he is immune to arrows while down at the portal. Keep repeating this until he is dead

Tips: Make sure you're prepared with full diamond gear, recommended to have it enchanted.

Pumpkin on your head stops you from annoying endermen

Water is useful to keep endermen away and also jumping down from the obsidian pillars into it.

Snowballs can destroy the crystals, grab a load of them.

The dragon spits purple poison, avoid it as it's really damaging.