Cropping the camera
A webcam gives you a wide shot of a room with a person somewhere in it. Usually you want the person.
On the Camera tab, Showing opens a crop box over the camera picture. Drag it to choose what part is shown. Reset puts it back to the whole frame.
The camera box on your canvas then takes the shape you cropped to. Crop to a tall rectangle and you get a tall camera; crop to a square and you get a square one.
What it is really doing
The crop works on what the camera actually recorded, not on the black bars a camera picture is padded with when it does not match the shape of its box. That sounds like a technicality and is the difference between a crop that lands where you dragged it and one that quietly drifts off the person's face.
Why it belongs to the recording
In a project with several takes, the position, the size and the layout of the camera are shared: one look for the whole video. The crop is not, and neither are the flips or the audio offset.
That is deliberate. Those three are facts about that camera on that day. If you moved your chair between takes, or plugged in a different webcam, the second recording needs its own crop and it should not undo the first one.
Belongs to at the top of the tab shows which recording's camera you are editing.