I agree with all the comments pointing out that an in-game tutorial would’ve been better, but I will try my best to explain it here. The core mechanic is the time manipulation (UI Slider on the top screen edge). Just drag that slider around to move through time. Then, at any point in (valid/not red) time, you can add a force to any physics-based object by just dragging. When you are done creating a force hit the play button (bottom left) to re-simulate the new timeline. If everyone survived you can move on to the next scene.