If you have purchased a game that requires Steam, please following these instructions to activate the game.
1) Launch the MacGameStore App and make sure you are logged into your account (top right corner).
2) Go to MY GAMES → PURCHASES and find the game. On the right side click on Play On Steam.
3) The screen will show you the Steam code required to activate a game on Steam. Click on Copy to copy it to your clipboard.
4) Click the Play on Steam button to launch Steam. If you don't have Steam installed on your Mac, the MacGameStore App will download Steam and install it for you.
5) On launch of Steam and this is your first time using Steam, it will ask you to login or create a new account.
6) Once you are logged into Steam, click on + ADD A GAME... in the lower left side of the Steam screen.
7) Then select Activate a Product on Steam.
8) Enter the Steam code by pasting the key you copied in Step 3.
9) Follow the on-screen instructions from that point to begin downloading and installing your Steam game!