See Help > Books > Essential Graphing for more details.
You can use the Line and Annotation tools to add these graphic elements to your plot with the mouse.
Alternatively, you can right-click inside the plot frame and select Customize. You will have to add some scripting expressions. The Pen Color( "red" ), H Line( x min, x max, 90 ), V Line( quantile, y min, y max ), and Text( CounterClockwise, "quantile" ) would be all you need.