Don't forget to spend your Planar Attunement XP on points in Planar Attunement. It gives you small stat boosts, the ability to summon your party/raid to a type of Rift and even a few buffs later on. You start to recieve Planar Attunement XP at level 50.
Click on the Player button at the botton left and choose Planar Attunement.
Slect one of the Planes using the buttons at the bottom and you will see a huneycomb design of buttons. Pick the one you want by clicking it. You can only unlock the extra honeycombs by completely fillling the one to it's left.
When you have unlocked multiple planes completely, the extra planes become available. (The small buttons at the bottom right in the above image) that have even more powerfull abilities.
Don't forget to press 'Save and Close' when done or your spent points wont be saved.