So, you've downloaded and cracked the seal on a fresh copy of Unity. You've seen some examples of what other people have done with the game engine, and you've taken a whirlwind tour of the interface. You can clear out the AngryBots Demo project by clicking on File | New Project in the menu. After choosing a folder for the new project (you can call it "Intro"), Unity may close down completely and start up again. Once it does, you're left staring at a 3D plane.