Everybody relies on you to destroy the hidden TNT. Luckily you are very good in doing so. Even when it is not as easy as it might seem, sometimes you need to open a door. Other times, you need to stop a door from opening, it takes all your brain to work it out. On top of that you need to avoid hitting the bomb with your bullet, because if you do hit it, the whole world explodes and you can start again.
Use the mouse to aim, the button to shoot. When you keep the mouse button pressed, you will see where your bullet goes.