The belt is supposed to lead to a backpack with some maliable substance as straps, that way anyone can wear it, not just humanoids. When you pull the trigger, the missile in the chamber locks onto the target the laser was pointing at when the trigger was pulled. Then, a short burst of compressed air shoots the missile forwards until it exits the barrel, then it may ignite (the air pushing it out of the barrel prevents the exhaust from damaging the user or the barrel). Fins for homing deploy once it exits the barrel. The missile has homing capabilities but unless it's a straight path, the missile won't hit the direct spot you were pointing at. If the missile loses the target from line of sight, it will go to it's last location and search. It's rather small so it doesn't have that much fuel, when the fuel runs out it detonates on the spot.
IT'S FREEE!!! GRAB SOME!!! Go boom the bots! @RainRaven for OLW Inspired by the belt fed grenade launcher and the missile pistol from Helldivers 2