What does 'play' mean in the context of Courser of Kruphix?
Courser of Kruphix uses the word "play" in two different ways. When it says


  Play with the top card of your library revealed.


It means that you play the game with the top card of your library revealed. That ability is a static ability, so it is in effect for as long as the Courser of Kruphix is on the battlefield.

On the other hand, when it says


  You may play the top card of your library if it's a land card.


That simply means that you can play lands on top of your library like your are normally able to do from your hand.