for those new this all this, "anchor" is where you want to end up and "control" is the point you would go to if you were drawing a square.
for example, this would draw a quarter circle
<?php
$s->movePenTo(100, 100);
$s->drawLineTo(200, 100);
$s->drawCurveTo(200, 200, 100, 200);
$s->drawLineTo(100, 100);
?>