Reference

How to understand 3D coordinates in the scene

Every element in the scene has a 3D coordinate that tells us the location of its center relative to the origin point, which is at 0,0,0. The three numbers in the coordinate represent the X, Y, and Z axis values respectively. When facing the origin point from the front, the X axis spans from your right to your left, the Y axis spans from up to down, and the Z axis spans from forward to backward. In each case, the value of the axis increases towards the former direction and becomes negative and decreases towards the latter direction once it reaches the origin point. Keep in mind that these directions are liable to change based on the rotation of your perspective.

In the example below, you can see both an origin point and a point that is located at (7, 3, 4). When viewing the origin point from the front, the point will appear to be 7 units to the right, 3 units above, and 4 units in front of the origin point. On the other hand, if we were to see a point that is located at (-7, -3, -4), it would appear to be 7 units to the left, 3 units below, and 4 units behind the origin point.