The camera tool is used to take in-session screenshots. If you find something interesting you want to share or look at later then the camera tool comes in handy. To activate it click on the Camera tool button on the Tool side of the menu. Once activated use the trigger button on the action controller to take a screenshot. You'll notice a brief fade to black (like a shutter) notifying that a picture has been taken. The picture will be a screenshot of the computer monitor meaning it will not ne a VR picture but a 2D one. The pictures are saved in the folder Output/<username>/<dataset>/Screenshots relative to where you installed CellexalVR. If you need help finding this folder, you can press the escape key on your keyboard to open the settings menu and at the bottom press "Open output folder", and navigate from there.
To deactivate the camera click on the Camera tool button again.