Only assignment, call, increment, decrement, and new object expressions can be used as a statement

If I can't declare it as a statement should I just wait until I need to use it? It's a very simple question ,but I need to know if I[m going about this the right way. How could I store hit.normal in a variable?

Here's the script:

 using UnityEngine;
 using System.Collections;
 
 //
 //THIS SCRIPT CONTROLS THE MOVEMENT OF THE PLAYER 
 //
 [RequireComponent (typeof (Rigidbody))]
 public class PlayerMovement : MonoBehaviour 
 {
     //ALL OF THE PUBLIC VARIABLES
     public float walkSpeed = 6.0f;
     public float runSpeed = 12.0f;
     public float jumpSpeed = 8.0f;
 
     //ALL OF THE PRIVATE VARIABLES
     private Vector3 moveDirection;
     private float speed;
 
     void Start () 
     {
         speed = walkSpeed;
     }
     void Update () 
     {
         moveDirection = new Vector3 (Input.GetAxisRaw ("Horizontal"),0, Input.GetAxisRaw ("Vertical")).normalized;
 
         RaycastHit hit;
         Physics.Raycast (transform.position, -Vector3.up, out hit);
 
         if (Physics.Raycast (transform.position, -Vector3.up, out hit))
         {
             hit.normal;
         }
     }
     void FixedUpdate()
     {
         rigidbody.MovePosition (rigidbody.position + transform.TransformDirection(moveDirection) * speed * Time.deltaTime);
     }
 }