First of all you need a
Glass Bottle. To make a Glass bottle you need
3 pieces of Glass. To get Glass you need to put Sand into the Ingredient section of the Furnace. Then cook it with a type of Fuel e.g. coal.
Find an End Portal, once inside the End, the Ender Dragon will occasionally fire his
Purple breath onto the floor. Have your Glass bottle
out in your hand and spam
. (would advise to make multiple Glass bottles so you can keep collecting the Dragons breath if it doesn't register first time)
You'll know you've done it if you've got the Dragon's Breath item in your inventory.
Another tip that would help is to have a pumpkin on your head so that the Endermen won't attack you.
Hope this helped.
Edit - Bernman 117 - "In the new tutorial world you can find an Ender Portal at X:172 Y:111 Z:106"