This website does not carry out any logging or tracking of your visits or activity on the site.
You do not need to install the libaries - you simply link to them from your web page (see documentation).
Download the documentation (PDF). Note that gMath.js and gPlot.js are both described in the one document.
Here are examples of lines, arcs, filled arcs, circles, polygons, straight text, and text on circles and ellipses - more than enough to draw a sundial. Below the drawing you will find buttons showing some of the kinds of other control you can use.