On paper, when I was learning Descartes’ coordibate system, we used Y as up and X as left-right. And when it was time to plot in 3D, we used Z to “extend” the plane into yourself and away from yourself.
You just hold your sheet of paper perpendicular to the ground (or just use a whiteboard) and it all makes sense.
Might depend on where you were learning.
On paper, when I was learning Descartes’ coordibate system, we used Y as up and X as left-right. And when it was time to plot in 3D, we used Z to “extend” the plane into yourself and away from yourself.
You just hold your sheet of paper perpendicular to the ground (or just use a whiteboard) and it all makes sense.