There is only one camera product listed on the store. If you are referring to the fact that there are 2 cameras in that picture, that is just a photograph. You receive exactly one camera module and one USB Cable for it.
I would recommend watching the LightBurn Camera Demo to best understand the functionality:
Within the camera product are different lens sizes, and you will have to make some measurements of your machine and do a calculation to find the right lens angle for your setup. You can consult these resources:
So yes, you are typically using the camera looking down with the lid open to line up your material and design.
Some machines use pegs or screws instead of hinges, and the door can slide left to right. This is not ideal. The gas pistons help to a degree. Check your machine and see how much wobble and repeatability is in the door when you open it.