Coroutine Loops

Coroutine Loops

Hi - I'm trying to understand coroutines (I come from Flash where you just run loops or use timers). I looked at this post:

http://answers.unity3d.com/questions/131858/instantiation-at-interval-times.html

but it doesn't seem to address looping. Nor does the documentation for unity - coroutines simply run and then finish. If I try to make a repeat call to the function from within the function, I get an error. Furthermore, if I move certain lines of my code out of update and into the coroutine function, I get errors. All I want to do is have a launcher which fires a projectile at a random interval every 5-10 seconds. This is my code, and I want to replace the dependency on the fire button with an automatic loop.

     function Update()
 {
     if( Input.GetButtonDown( "Fire1" ) ){
         var randomAngle:float = Random.Range(120, 180);
         var randomRot = Quaternion.Euler(0,Random.Range(-30, 30),-10);
         launcherRef.transform.rotation = initialRot * randomRot;
         
         var numRandom:float = (Random.value*objectSizeMax);
         //instantiate a projectile and throw it toward the cube (x axis)
         var instantiatedProjectile : Rigidbody = Instantiate( projectile, transform.position, transform.rotation ) ;
         instantiatedProjectile.transform.localScale = Vector3.one * (numRandom); //I add these two together here because I have no clue what I'm doing
         instantiatedProjectile.velocity = transform.TransformDirection( Vector3( speed, 0, 0) );
         for (var i=0; i<boundaryRef.length;i++){
             Physics.IgnoreCollision( instantiatedProjectile.collider, boundaryRef[i].collider); //make sure to ignore collision between launcher and missile
         }
     }
 };