Just put both ends in the slots and push down until both sides click. It doesn’t lock other than by friction with the tailgate.
You can also fit your hands up under each side along the bed rails and air will get in there at 75 mph down the road.
I’ll try to post some pics tomorrow.
I’ve noticed it’s almost the same amount of noise either way. But I run down the highway at 75 with mine back and the window out, it does fine. I was worried at first but it hasn’t flew off yet.