Hovering over a point on a line will reveal specific information about that data point.
The icons above and to the right of a chart's title are tools you can use to zoom in and out.
To reset the view, click the home icon, or double click inside the chart.
The camera icon will allow you down download a png image of the chart.
To hide a line, click on it in the legend.
To add a line back, click on it in the legend again.
The graph will be remade to show only the lines you've selected.