On the first page, the top graph shows how the graduation rate has changed over time. The horizontal axis is for each freshman cohort. For example, "2013" indicates the freshman class of 2012-13, who would graduate from high school in 2016, if they finished in four years. For older classes, there is an additional line representing students who graduated from high schools in six years. (Six year graduation rates are not available for more recent classes). The bottom graphs break out the proficiency rates by various student groups. You can filter all these graphs by district and school. You can also change the year of the breakout graphs on the bottom. Hovering over the graphs shows more information.
The second page allows you to compare two different graphs.