Overview from the game manual:
XS is an absorbing combat experience. The action takes place in an arena where you battle with several other competitors and fight to the death. The arena can be any enclosed are and contains a number of hostile drones, mobile turrets and other hazards. All competitors use hard-light shields and these shields must be depleted before the competitors can be killed. Rules regarding weaponry are simple - anything goes, including stealing dead player's guns. All competitors are allowed one infinite-ammunition weapon which is usually a hand-blaster of some sort. Additional supplies of heavier ammunition are dotted around the arenas or carried by the drones. You can select your difficult level before you enter the game. If you choose easy mode, then a map is shown in your heads up display. In hard mode, the computer controlled characters tend to fight you rather than each other.