Double-click the flag. Click the Start button to begin. WASD moves your tank (the orange one at the bottom), and you use the mouse to point and click to shoot. Go to the blue portal to win.
There is audio. It most likely will glitch out a lot. When that happens, restart the program. If the turret does not work, which it almost invariably won't the first time, restart. I WISH I HAD MORE TIME!!!
