On the first page, the top graph shows how (1) the number of AP test takers, and (2) the amount of college credit obtained as a result of AP exams, has changed over time. The bottom graphs break out college credit and test taker rates by various student groups. You can also change the year of the breakout graphs on the bottom. Hovering over the graphs shows more information. All of these graphs are representing cohorts of students, and cohort refers to a group of students who entered high school in 9th grade at the same time and graduated four years later.
The second page contains graphs that show AP Exam Subjects, and you can break out this information by both district and various student groups.