OnCollisionEnter is called when this collider/rigidbody has begun touching another rigidbody/collider.

In contrast to OnTriggerEnter, OnCollisionEnter is passed the Collision class and not a Collider. The Collision class contains information about contact points, impact velocity etc. If you don't use collisionInfo in the function, leave out the collisionInfo parameter as this avoids unneccessary calculations. Note that collision events are only sent if one of the colliders also has a non-kinematic rigid body attached.

	function OnCollisionEnter(collision : Collision) {
		// Debug-draw all contact points and normals
		for (var contact : ContactPoint in collision.contacts)
			Debug.DrawRay(contact.point, contact.normal, Color.white);
		
		// Play a sound if the coliding objects had a big impact.		
		if (collision.relativeVelocity.magnitude > 2)
			audio.Play();
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnCollisionEnter(Collision collision) {
        foreach (ContactPoint contact in collision.contacts) {
            Debug.DrawRay(contact.point, contact.normal, Color.white);
        }
        if (collision.relativeVelocity.magnitude > 2)
            audio.Play();
        
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnCollisionEnter(collision as Collision) as void:
		for contact as ContactPoint in collision.contacts:
			Debug.DrawRay(contact.point, contact.normal, Color.white)
		if collision.relativeVelocity.magnitude > 2:
			audio.Play()

OnCollisionEnter can be a co-routine, simply use the yield statement in the function.