[from wikipedia : http://en.wikipedia.org/wiki/Double_Dragon]
The player takes control of martial artist Billy Lee, or his twin brother Jimmy (also known as Hammer and Spike in the supplementary materials for the American arcade release), as they fight their way into the turf of the Black Warriors gang in order to rescue their common love interest Marian. The player character has a repertoire of martial art techniques which they can perform by using the joystick and three action buttons (kick, jump, and punch) individually or in combination. Techniques ranges from basic punches and kicks, to more elaborate maneuvers like hair grabbing moves or elbow punches. When playing with another player, one can assist the other by grabbing their partner's opponent from behind. The player begins the game with a certain number of extra lives and a life gauge which depletes as the player takes hits from enemies. If the life gauge runs out or the time limit reaches zero, the player will lose a life.
There is a small variety of enemy characters that the player will face thorough the course of the game. Certain enemies will carry a melee weapon which the player can use by disarming the enemy carrying it and then retrieving the item from the floor. The available weapons includes steel bats, whips, throwing knives, and dynamite sticks, as well as large objects such as cardboard boxes, oil drums, and logs, which the player can lift and throw at enemies or kick it towards incoming ones.
The game is divided into four different stages or "missions", which consist of a city slum, a factory, the woods, and the hideout of the boss. The game normally ends if a single player defeats the final boss alone. However, if two players manage to complete the game together then the two will be forced to fight each other in order to determine who will win Marian's affections.