Players shoot in turns.
To shoot at the other side, press shoot button. Fired ball bounce around and disappear after 4 explosions, or after it hits the other player, or after it goes out of side view boundary. If you choose angle zero you will sure kill yourself. If fired ball hits the top of the screen or side of building, it will not explode, but only bounce. With all the bouncing around it is much easier to kill yourself than your opponent.