This is how I understand this:
The verb is capire - to understand
In it's present tens (now), singular, first person form it is: Io capisco - I understand
In it's passato prossimo tens (resent) it is Io (ho) capito - I have understood
So you should use "capisco" if you are understanding what is being discussed right now . .
And use "capito" if your process of understanding has been completed . . resently.