public class PlayerController : MonoBehaviour {

    private Rigidbody rb;

    // Use this for initialization
    void Start ()
    {
        rb = GetComponent<Rigidbody>();

    }

    // Update is called once per frame
    void Update ()
    {
        float movementHorizontal = Input.GetAxis ("Horizontal");
        float movementVertical = Input.GetAxis ("Vertical");

        Vector3 movement = new Vector3 (movementHorizontal, 0.0f, movementVertical);
        rb.AddForce = movement;
    }
}