[jitter] Basic Question

I have a few basic questions relating to drawing basic shapes (and maybe a few not so basic ones) using sketch/openGL. First and for most I need to know the basic principles on how to draw circles and arcs. I have looked at the jitter tutorial concerning sketch, and I see how to draw triangles and squares, and the derivatives there of, but how about basic circles and arcs? Also, I need to be able to draw basic representations of wave shapes as lines, such as a sine wave from one point to another based off the frequency of A cycle~ object. This line needs to reflect realtime change also... quick response would be awesome, as I am on a school deadline.