A CFrame consists of an offset (the Position, or P vector) and 3 basis vectors XVector, YVector, ZVector. These 3 vectors define the rotation by establishing a right, up and back (-Z is forward in roblox) direction. When these 3 vectors are all perpendicular, the camera behaves normally. Bending these vectors away from perpendicular is what causes the skew. Keep in mind that there is a second matrix used by the camera, the Projection matrix, that you can’t directly edit. It is controlled by the FoV and near / far distances.
When you start out in Camera Skewer, note that each vector has one component which is 1, corresponding to its axis. I.e. R11 starts as 1. Changing the vectors that were originally one scales the view inversely in that direction. If you set R11 to 0.5, then 1 unit of vertical space only takes up half the vertical distance on screen, so your view squishes vertically. Changing a value that was originally zero causes cross-coupling between horizontal and vertical, skewing the view.
Keep in mind that this example is actually letting you multiply the camera basis vectors, not set them. The basis vectors change continuously as the camera is rotated.
(This part is wrong but I have to brb so I can’t fix it now):
A yVector multiplier of 0.5, 1, 0 would actually mean cameraMatrix += cameraMatrix * Vector3.new(0.5, 0, 0)