forward

Move forward by the z component of vector in the direction of the normal, and also shift across by the x and y components of vector (using the normal's direction as our coordinated system).

For example, if the normal is (0,0,1), then forward would do exactly the same of moveBy, i.e. current position = current position + vector.

However, if the normal was (1,0,0) (pointing along the X axis instead of the Z axis), then then vector.z would move us along the X axis, vector.x would move us along the Z axis, and vector.y would move us along the Y axis.