how to make grabbing in unity code example

Example: Hand Grabbing Script

using UnityEngine;
using System.Collections;

public class GrabObject : MonoBehaviour {

    public GameObject hand;

    private GameObject grabbedObject = null;
    private Transform objectOrgParent = null;

    void OnCollisionStay(Collision collision) {
        if (Input.GetMouseButton(0) == true) { // Hand is closed
            // the object we grab
            grabbedObject = collision.gameObject;
            // Make it kinematic as we are holding it now
            grabbedObject.rigidbody.isKinematic = true;
            // Store the original parent to restore it when letting loose
            objectOrgParent = grabbedObject.transform.parent;
            // And parent it to the hand
            grabbedObject.transform.parent = hand.transform;
        }
    }

    void FixedUpdate() {
        if (grabbedObject != null) { // are we holding an object?
            if (Input.GetMouseButton(0) == false) { // Hand is open
                // unparent it from the thumb
                grabbedObject.transform.parent = objectOrgParent;
                // make it non-kinematic again
                grabbedObject.rigidbody.isKinematic = false;
                // and clear the grabbed object
                grabbedObject = null;
            }
        }
    }
}