Use the arrow keys or WASD to move. Use the mouse to aim and click to shoot. Don't touch the dark colours around the edge of the stage! Red cubes damage you 1 HP. Shoot them to gain 1 point. Red stars damage you 5 HP. Shoot them to turn them into yellow stars. Yellow stars give you 10 points on touch. Also, the immobile fruits will heal you. Red fruits heal you 1 HP, yellow fruits heal you 5 HP and blue fruits heal you 10 HP. Watch out for the slightly darker fake fruits! There are more things than the ones listed above, but those are the ones I will give away to you at the start.
Credit to @-Multinia- for both text engines.