First of all, you put
var motion in
_physics_process() so now you have a new local
motion variable that has no value. Delete this line. You've already declared the
motion variable as a class variable at the top.
Second, normalizing is a function performed on vectors. It means taking a vector and scaling its length to 1. So for example the vector
(1, 1) would become
(0.707, 0.707). However, you can't normalize only the x component.
Finally, you're never assigning any value other than
(0, 0) to
motion so your body is never going to move in the
If you're new to working with KinematicBody2D, I recommend reading the following:Using KinematicBody2D
Also, for understanding vectors, I highly recommend reading this: