Question about ground and front "locking" wire on Floodlight Wired

I got a floodlight wired (no cam) and was curious how exactly the floodlight is grounded since there's no ground wire? The bracket has a ground hole but the instructions say not to attach the ground wire to the bracket, only the junction box. How exactly is the floodlight grounding then? Also, what exactly is the metal screw on the front of the floodlight, the one next to the picture of the lock/unlock?