can any body explain this rumba please

Hi

I can't figure it out look at this video

http://www.youtube.com/watch?v=MilvUL-8bwY

I am confused about the "p" finger

I understand that

P goes down then comes up
then 4 fingers together strike and P strikes while coming up
then you holde the strings

And from here I am confused
the 4 fingers are striking and coming up or the p finger

Is there an chart for this please?
Can any body explain it?