Converting a span to a Bézier curve enables you to alter the appearance of a linear or an arc span within a vector.
When you convert a span to a Bézier curve, two control points are placed on the span, both of which can be dragged to add or reduce the curvature within it.
To convert a span into a Bézier curve:
For example, your converted span may look something like that shown below:
Although this span may not look like a curve now, the two control points indicate that it is a Bézier curve span.
By dragging the control points as shown below, a Bézier curve span with a smooth curvature is created: