how to use on collision enter unity forum code example

Example: unity on collision enter

using UnityEngine;
using System.Collections;public class ExampleClass : MonoBehaviour
{
    AudioSource audioSource;    void Start()
    {
        audioSource = GetComponent<AudioSource>();
    }    void OnCollisionEnter(Collision collision)
    {
        foreach (ContactPoint contact in collision.contacts)
        {
            Debug.DrawRay(contact.point, contact.normal, Color.white);
        }
        if (collision.relativeVelocity.magnitude > 2)
            audioSource.Play();
    }
}