please explain controlled afib and aflutter

"Controlled" A-fib or flutter generally refers to whether the ventricular heart rate is controlled, ie whether the rate is not excessively high.  What rate might be "uncontrolled" is not standardized, but generally refers to a rate that is detrimental to the patient's hemodynamics.

In a "normal" sinus rhythm, the sinus node determines the patient's heart rate, in response to a variety of physiological feedback mechanisms, by initiating an electrical signal in the atrium which then travels to the ventricles resulting in a complete contraction of the heart.  

In A-fib or Atrial flutter there are sources of electrical impulses in the atria that have gone rogue and are generally very fast.  Luckily, the AV-node blocks many of these impulses, and ventricles have not had sufficient time to repolarize to match the atrial rate.  Despite that, the ventricular rate may be too fast to be hemodynamically effective (no filling =  no output) so the rate may need to be further "controlled" which we do primarily with medications that further block conduction through the AV-node.