For third-person games, movement usually follows camera orientation.

Vector3 forward = cameraTransform.forward;
Vector3 right = cameraTransform.right;

forward.y = 0f;
right.y = 0f;

forward.Normalize();
right.Normalize();

Vector3 direction =
    forward * input.y +
    right * input.x;

Then move with your chosen system:

controller.Move(
    direction *
    speed *
    Time.deltaTime
);