When you download the free Activision Anthology app, you receive Kaboom! as the only unlocked game. From there, you can purchase four different 11-game packs to complete your collection.
To access the purchase menus, scroll to any of the unlocked games and tap the Details button in the upper right corner. This will reveal the 11-game pack in which that selected game is included. Every 11-game pack Details page also includes a “Buy the Complete Collection” button.