Your first question is somewhat ambiguous. No weapons can currently kill you, the player, as only player-v-creature combat is currently implemented. In that respect, lightsabers can be used to attack and kill creatures. They behave like any other weapon, albeit one that is difficult to obtain.
Stun cuffs are used to arrest other players or NPCs. You equip them to one of your hand slots and approach whoever you want to arrest. The rules and conditions regarding that process can be found here