In this predecessor to Night Raid, you control a fixed turret with which you shoot down enemy flying vehicles that scroll by randomly on the top of the screen.
Helicopters drop paratroopers, who, if they make it to the ground without you shooting them out of the air, will attempt to overwhelm your turret. 4 paratroopers on either side will spell doom, as they build a human pyramid and reach the turret. Or, if just one paratrooper lands on your turret, it's game over as well. Helicopters will explode into shrapnel, which might take down other helicopters or paratroopers. Jets drop bombs which can be shot as well. If just one bomb hits, it's over.
Shooting enemies adds points to your score, but each shot substracts points, so you want to fire as conservatively as you can manage. Later levels get crazy with enemies, so unless you're Data, your best bet is just to spray n' pray, regardless of your shots costing you points.