Aim with the circle. Shoot with space. If you run out of energy you will die. If the asteroids touch the Earth then you will lose. The energy is mostly there for you to not spam. Keep an eye on the energy. An alarm will sound if you have only 20 energy left.
This is an updated version of an older game I made: https://scratch.mit.edu/projects/1133521695 I hope you like the new version!