Need help identifying ground screw
Those bare copper wires are the safety ground wires. The ground wire from the light needs to connect in with those bare copper wires. 

The best way to wire it in would be to free the two wires that are there now and use a wire nut to join the two bare wires, the one from the light and an additional short pigtail. The other end of the pigtail would go under that box grounding screw. The pigtail should be either a bare copper wire or a green insulated length of wire. It should be the same gauge as those already in the box.