how can I make an explosion?

Questions & Answers
1

am new to unity i used this script to shoot a projectile from my rocketlaucher:

var projectile : Rigidbody;
var speed = 20;

function Update () {

     if ( Input.GetButton ("Fire1")) {

          clone = Instantiate(projectile, transform.position, transform.rotation);
          clone.velocity = transform.TransformDirection( Vector3 (0, 0, speed));

          Destroy (clone.gameObject, 15);
      }
 }

when my projectile hits another object i whant it to make an explosion

can anyone help plz;

2

Instantiate an exlosion prefab when the rocket hits an object.

function OnCollisionEnter(col: Collider){

  var Explode : Transform;
  Instantiate(Explode, transform.position, transform.rotation);

}

That should work as a basic Instantiate script,attach it to your rocket. and download some explosion prefabs from here:
http://unity3d.com/support/resources/unity-extensions/explosion-framework.html

3

Creating an explosion on collision with another gameobject is essentially a two step process:

  1. detect the collision
  2. instantiate your explosion effect (generally a particle system of some sort)

The second link there even goes over explosions specifically. Good luck with your project!