Shoot Script Reload Help

Hey I need help with reload. I want it so after you press the reload button (r) you can't immediately shoot after that. I'd also like it so the amount of time after you press r till you can shoot again to be a variable. Now I don't want you to give me a straight up script, I'd like if you could step by step teach me how to do this. Here shoot script,

 var prefabBullet:Transform;
 var shootForce:float;
 var shots : int = 0;
 var maxShots : int = 30;
 var shootSound : AudioClip;
 function Update()
 {
     if(Input.GetMouseButtonUp(0) && shots < maxShots)
     {
         var instanceBullet = Instantiate(prefabBullet, transform.position, Quaternion.identity);
         instanceBullet.rigidbody.AddForce(transform.forward * shootForce);
         audio.PlayOneShot(shootSound);
         shots++;
     }
     else if (shots <= maxShots && Input.GetKeyDown(KeyCode.R))
     {
         shots = 0;
     }
 }