The two bare wires are your ground wires, but they are not installed properly according to current codes (even though as long as the screws remain tight it should provide sufficient fault protection).

To be installed properly, there should be a "pigtail" from under one of the screws in the back of the box connected with a wire nut to the two ground wires AND the ground wire from your light fixture. That's a total of four wires in a wire nut.

The one on the left is horribly short. The one on the right is even shorter. Since you may be unable to connect them properly, you can try leaving the one on the right as is. There may be enough slack on the one on the right that you can pigtail it as described above (three wires in a wire nut).

Under no circumstances is it acceptable to put more than one wire under a screw. It's nearly impossible to get a solidly reliable connection with more than one wire under a screw.

If you find it impossible to use a wire nut because the wires are so short, go to Home Depot or Lowes and get some push-in connectors. They're similar to wire nuts, except you push the wires into holes (one wire per hole) like into the back of an outlet. (I don't like the "backstab" connections on outlets, and I'm suspicious of these connectors, but in this situation it may be the best option.)

The two bare wires are your ground wires, but they are not installed properly according to current codes (even though as long as the screws remain tight it should provide sufficient fault protection).

To be installed properly, there should be a "pigtail" from under one of the screws in the back of the box connected with a wire nut to the two ground wires AND the ground wire from your light fixture. That's a total of four wires in a wire nut.

The one on the left is horribly short. The one on the right is even shorter. Since you may be unable to connect them properly, you can try leaving the one on the right as is. There may be enough slack on the one on the right that you can pigtail it as described above (three wires in a wire nut).

Never wrap more than one wire under a screw. It's nearly impossible to get a solidly reliable connection with more than one wire under a screw, unless it's the type that has a clamping plate and is designed for more than one wire, but in that case you're not wrapping the wire around the screw.

If you find it impossible to use a wire nut because the wires are so short, go to Home Depot or Lowes and get some push-in connectors. They're similar to wire nuts, except you push the wires into holes (one wire per hole) like into the back of an outlet. (I don't like the "backstab" connections on outlets, and I'm suspicious of these connectors, but in this situation it may be the best option.)