Zap'em is an action game for one player. You control a spaceship on the left side of the screen which is capable of moving up or down and firing lasers. Coming towards you from the right will be numerous enemy ships. You need to shoot as many of the enemies as you can in order to earn points. While many of the enemy ships take only one shot to destroy, some will require multiple hits and a few will even be ghost ships and can disappear temporarily. Your ship has a limited amount of fuel which will steadily decrease; the game ends when you have no more fuel left.