If you have no games, then every day you will get 1 new game. However, you cannot accumulate the games which means that if you do not use the game that you just earned, it will disappear. Fortunately, you get another one at tomorrow. Better use it! If you are on paid games, which I assume you are, you shouldn't even need this feature.
I am still confused if you get one even if you still have games going. The info about that might be inaccurate, but please forgive me. Remember that this post is coming from someone who is not on paid games.
If you don't want to risk it, be sure to check out chapter 2 of the
game guide before you continue playing.