Used WASD or arrows to move, and space or click to shoot. Use the mouse to aim and look around. Press R to reload. Your kill count is displayed under your name and resets when you die. Players have 20 HP and heal 1 point every 4 seconds if they have not been damaged for at least 4 seconds. Each hit does 1 damage, and guns rapid fire 10x per second.
It is very unlikely that there will ever be other players on unless you invite them. If you are a New Scratcher, you won't be able to play, but you'll still be able to move around the world. Turbo mode is not supported. You can play with two clients of the same name only if no other users are online. This game calculates if a player was hit on both your computer and your opponents, if you hit someone on your screen, chances are you will hit them on theirs. Basically if I hit you on my screen, my player will use an aimbot on your screen unless there is a wall in the way. This shooting prediction works for at most 3 players for any given shot, so if you fire at a whole row of players that are moving you may miss some. Credit to @bobbyguy1 for the gun picture.