,Please help me with CharacterController.isGrounded

Could You PLEASE tell me where is my problem in this code

I'm trying to move my player when he's Grounded only , Otherwise Not so I wrote this

   ||
  \\ //
    \/

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class PlayerMovement : MonoBehaviour {

 CharacterController controller;
 public float speed = 5f;
 float zAxis;
 float xAxis;


 // Start is called before the first frame update
 void Start()
 {

     controller = GetComponent<CharacterController>();

 }

 // Update is called once per frame
 void Update()
 {

     if (controller.isGrounded)

     {

         // Taking Inputs From User //

         zAxis = Input.GetAxis("Horizontal");
         xAxis = Input.GetAxis("Vertical");

         // Adding Speed Controll //

         zAxis *= speed;
         xAxis *= speed;

         // Adding Time.deltaTime //

         zAxis *= Time.deltaTime;
         xAxis *= Time.deltaTime;

         // Adding Movement To Player //

         transform.Translate(xAxis, 0.0f, zAxis);


     }

 }

} ,Could You PLEASE tell me where is my problem in this code

I'm trying to move my player when he's Grounded only , Otherwise Not so I wrote this

   ||
  \\ //
    \/

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class PlayerMovement : MonoBehaviour {

 CharacterController controller;
 public float speed = 5f;
 float zAxis;
 float xAxis;


 // Start is called before the first frame update
 void Start()
 {

     controller = GetComponent<CharacterController>();

 }

 // Update is called once per frame
 void Update()
 {

     if (controller.isGrounded)

     {

         // Taking Inputs From User //

         zAxis = Input.GetAxis("Horizontal");
         xAxis = Input.GetAxis("Vertical");

         // Adding Speed Controll //

         zAxis *= speed;
         xAxis *= speed;

         // Adding Time.deltaTime //

         zAxis *= Time.deltaTime;
         xAxis *= Time.deltaTime;

         // Adding Movement To Player //

         transform.Translate(xAxis, 0.0f, zAxis);


     }

 }

}