Your game must first be published on the Gametize dashboard. See: How do I 'publish'/'unpublish' a Project/Topic/Challenge?
Once published, your game is accessible via the Gametize app (Available on iOS/Android via http://gametize.com/app or search "gametize" in Apple's app store and the Google Play store).
Your game is also accessible via web browsers, with the link http://gametize.com/game/YOURGAMECODE. See: What is a game code?
Your game can also be published as a white-label mobile app on request. Please contact firstname.lastname@example.org to enquire on the pricing.