Depending on your platform, the process varies slightly. Here is the for each system.
Acts I through IV of the original Diablo III story.
This is not optional. The base Diablo III (often called "Vanilla" D3) ends at Act IV, with a level cap of 60. added:
You must complete at least one Greater Rift on your account to unlock this weekly rotating mode, which offers massive material rewards. 4. Kanai’s Cube
During sales (which happen every few months on Steam for consoles or Battle.net for PC), the Eternal Collection drops to . For ten dollars, you get:
Diablo III: Eternal Collection includes the game, Reaper of Souls, and Rise of the Necromancer, giving immediate access to the top content most players want. Unlocking is primarily a matter of purchasing/installing the edition, keeping the game updated, and creating the appropriate characters (Seasonal or Regular). For additional paid cosmetics or platform-specific packs, redeem via your platform store and restart the game.