ADP represents Average Draft Positions in fantasy football drafts. It can serve as a useful draft prep tool in assessing players' values, and knowing what round / pick you might want to invest in them...
PPR refers to a Point Per Reception. Each reception made by your fantasy team earns one extra point. PPR leagues give you extra fantasy points every single time a catch occurs.
Various fantasy leagues allocate different points for a receptions with a varying range between .5 (half point PPR) and 1.5 points (Tight End Premium). Check with the league commish to see how many points you receive before the season starts, as this will affect your decision-making strategy.