Use W/S or arrow keys to move your square up and down. Don't get pushed back into the edge by the blocks! You start out with three bullets. Press space to fire them. You can get more bullets by collecting the blinky gray dots that appear every now and then. Your score is based off of how many blocks get past you.
The highest possible score is 999. Try to bet my high score of 369! Pixel Pushback 2 - https://scratch.mit.edu/projects/248422417/