Calling OnCollisionEnter

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {

void OnCollisionEnter2D(Collision2D coll) {
    if (coll.gameObject.tag == "Enemy")
        coll.gameObject.SendMessage("ApplyDamage", 10);

Here is the example of OnCollisionEnter given by unity how would I call this function to check for collision as if I write OnCollisionEnter2D() it says it doesn’t take zero arguments what should be put as The argument?
Thank You.

Oh good you are trying to learn from Unity tutorials.

In Unity , you dont need to call these functions manually.They are called by unity itself when a collision is detected.

If you need your Gameobject should react to the physics you need to Add Rigidbody2D component.
(Just make sure both GameObject have got Colliders.)