This is a tool with a ball on each end, one small and one large.   It is usually made of plastic, but is available in metal.

The ball tool is used to shape the petals of sugar flowers to make them thiner and, in the case of rose petals, curved.  Holding the petal in the palm of one hand, gently roll the ball tool around the edges of the petal until you have the desired thickness and shape.

The tool can also be used in many other ways such as shaping the faces on sugarpaste or marzipan animals and the small end makes good indents for eyes.