When a user sends you an invitation to a new game, you will have the possibility to reject the invitation in case you do not want to play.
New classic games will be seen in the "Games" tab. To do this, you must go to the section of the game represented by a list, located as the second option in the bottom bar of the screen. When you see the invitation that has been sent to you, a pop-up will be displayed where you can reject or accept the game.
Keep in mind that rejecting a game before starting to play will not affect your game statistics, although it may appear as "lost".