Currently, the folding pool pays out a certain amount of Curecoins per day, right now 7488 coins. The PPD represents the points that you earned in the last 24 hours, and is used in calculating the distribution. Say, for example, that all Curecoin folders combined folded 10,000,000 Points yesterday, and you folded 100,000. You would get 1% of that day's payout, which would account for 74.88 CUR.