Use the WASD to move and left-click to shoot your gun. Monsters will spawn from the top and your goal is not to get eaten by them. The monsters are not very smart but when they sense you, they catch you fast, so be careful. Killing a monster increases your kill count which is at the top right corner. Your health bar is at the top left corner If you are low on health, wait for a first-aid kit to spawn. Its healing factor is not instant.
If there are any bugs, comment them. Suggestions are open. And enjoy!