Games can be public or private. You have the ability to choose if you'd like to put a password on your game to make it private, or if you'd like to leave it open for anyone to join!
Note: There are a few parts of your game that are always public for those who are searching for your game, such as the game title, description, and game picture. However, all other aspects (missions, submissions, etc.) can be kept private by adding a password to your game.