I never really knew what they were for but I was reading a Clancy novel and he said they are made of glass that will stop a .50 caliber round. The teleprompter actually sits over the camera lens with the text slanted like a rear view mirror on night setting.
The technology has advanced considerably since my day. Back then there was a box with a motorized scroll (with large type face), lit and mounted under the camera lens. It added considerable front weight to an already heavy camera atop a counterbalanced dolly. I imagine the whole package might have weighed around 800-1000 lbs... and that was a black and white camera.
These new color cameras are about the size and weight of a Whitman's box of chocolates. The teleprompter text, I presume, is on a bright flat screen tv mounted under the camera lens (or over) with a reflective transparent screen mounted in front of the camera lens angled so that the speaker is looking directly at the viewer as he/she reads the text.
At public appearances, such as Trump rallies, the cameras are relatively far removed. You will notice two clear plastic sheets on each side in front of the speaker's podium set at a downward angle. The crowd can see the speaker through the clear panels, but a 'projector' below the plastic panels shines the text which is reflected so that the speaker can read it while moving his eyes back and forth looking at the audience. The cameras are no longer part of the procedure.
The 'bamster was so dependent on the teleprompter that he actually used the set up to address a sixth grade class at one time.
As to the bullet protective sheets, much research has gone into the matter, and the technology is evolving. We see thick sheets set up at banks, but I suspect that is cheaper old technology. I have seen some impressively effective thinner materials on some TV shows. But I am basically talking through a cocked hat on this subject. 😐