Well, the part at the front is the barrel, where the bullets come out.
Okay, so the barrel is slab-sided and grip-taped to help hold onto the edge of the barricade. The black "crossbar" thing is a barricade wing, which gets shoved into the barricade. When the barrel and barricade are gripped by the gun and your off hand, everything is locked in tight and you can just go crazy without worrying about trigger pull or grip or any of that other nonsense. The black stuff on the wing is Plasti-dip - when the wing was bare steel it once slipped during the string and I machine-gunned most of the cylinder into the dirt. No prize table that day!
The bit under the sight is for shooting the mover. You pull out the black handle at the rear of the base and slide it left or right, depending upon which direction the mover will be going. That moves the sight just the right amount so that you don't need to lead the target - just hold on the black and have at it. I always had trouble with the mover, but that sight base allowed me shoot three or four perfect scores on that match.