Wait for seconds usage?

Hey. I am having trouble using “yield WaitFotSeconds”. The script seems freeze once I try to wait (but if I take out the yield statement. What is wrong?

var Enemy : GameObject	[];
var Time  : int			[];
var Position : Vector3  [];
var List: GameObject	[];
var test               = 0; 

function Update (){
	if (Input.GetKeyDown ("k")){Invoke("TESTING",0);
	}
}

function TESTING (){
		for (var i : int = 0;i < Enemy.length; i++) {
			 yield WaitForSeconds (3);List<em>=Instantiate(Enemy_, transform.position+Position*, transform.rotation);*_</em>

* }*
}

You can’t Invoke coroutines.