Question

I want the circle with box2d in video.
http://goo.gl/39Ff3

Answer 1

Did you check this site? There seems to be much tutorials.

And don’t forget the manual especially 4.2 Circle Shapes.

Circle Shapes
Circle shapes have a position and radius. Circles are solid. You cannot make a hollow circle using the circle shape.

   b2CircleShape circle;
   circle.m_p.Set(2.0f, 3.0f);
   circle.m_radius = 0.5f