it's in Japanese, but basically the goal is to remember which numbers are where, and click the LOW ONES first after they're replaced with circles. so if you see 7, 3, 8, 0 click the circles in order 0, 3, 7, 8.
then it tells you how old your brain is.
I got a 31, 26, 28... all pretty close to my real age which is funny.
i'm going to do it next year so i can tell if i'm slowing down.