Courser of Kruphix doesn’t change when you can play lands. You can do so only during your main phase when you have priority and the stack is empty.

Playing a land with the second ability counts as your land play for the turn. If you play a land from your hand during your turn, you won’t be able to play an additional land from the top of your library unless another effect allows you to.

The last ability triggers whenever a land enters the battlefield under your control for any reason. It triggers whenever you play a land, as well as whenever a spell or ability (such as Rampant Growth) causes you to put a land onto the battlefield under your control. It will even trigger when a spell or ability causes another player to put a land onto the battlefield under your control (as can happen with Yavimaya Dryad’s ability, for example).

While playing with the top card of your library revealed, if you draw multiple cards, reveal each one before you draw it.