Aquatix aqua cam expedited underwater video housing

This is an aquatic video housing holder, to be honest I know nothing about it. It was in my garage when I bought my new home, I know that my previous owner was into underwater photography and scuba diving and I read up and this is a canister to hold a camera Please note inside it has a screw that is rattling around. I didn’t wanna undo it and try to screw it back on not knowing exactly what I’m doing.