Instructions
Open "Starcraft 2."
Select "Multi-Player" to open the Quick Match page.
Click "Create a Game" under Custom Games to open the Create Custom Game page.
Select a game and click "Create Game" to open the Game Lobby.
Select your opponents. Make sure you choose to play the Terrans.
Click "Start Game."
Select your Space Construction Vehicles.
Instruct your SCVs to start harvesting the nearby minerals until you have enough to build a Supply Depot.
Select one of your SCVs and have it build a Supply Depot.
Select a different SCV and have it build a Barracks when you have enough minerals to do so.
Select the SCVs building the Supply Depot and Barracks. When they finish their construction projects, have them return to mineral harvesting.
Select your Command Center and construct a new SCV.
Select your Barracks when it is available.
Build two Marines. You should have enough minerals to do this.
Select the Barracks.
Build a new Marine.
Select an SCV and have it build Barracks.
Build five Marines from your first Barracks.
Build the remaining three Marines from your second Barracks when it is available. You should still be within your time limit when your Barracks finish building Marines, earning the Training Day achievement.