no your brain was lost but its ok not everyone was meant to get everything hence these forums.
it does NOT reduce the cooldown of current ever. its ALWAYS from base. if you kept all your gold and bought enough items with cooldown reduction to equal 40% all at the same time starting with an ability cooldown of 10 seconds you would get 40% from 10 seconds aka a 6 sec cooldown. you would not have to suffer selling items and rebuying them to get the best cooldown that would be silly.
cooldown reduction is additive to itself and is always based off of the original cooldown timer. if the cooldown was 100 seconds and you lower it by 5% then 10% then 15% the cooldown would be 70 seconds or 30% CDR.
He's talking about abilities that reduce your cooldown. Like Zilean's Rewind and Ryze's passive.