ya know it might be a setting but I believe those numbers are:
vp# = # of hands voluntarily entered
pr# = # of hands raised
af# = # of hands won???
I think this is right. Although I have used Pokertracker in the past I never really got to into it, mostly because I don't play a ton of hold em. I am pretty sure that is what those numbers mean but someone else might have a better answer.