You can use W, bar or up arrow to go up and S and down press space bar to shoot a bullet and it will give you one point if you hit the thing arrow to go down you have to jump every 0.65 seconds. If you want to just practice go to settings and click practice mode you cannot die and cannot gain score unless you press the Q key
For the boss battle at the end you have to get lucky and pray for the boss to not go down! There is your high score and the world record score