How do the people who make 'Hula Hoops' make them in that ring shape?

I have seen similar products made, so Hula Hoops are probably the same. Imagine a tank full of the paste that the hoops are made from, and in the side of the tank is a hole the diameter of a hoop. Outside the tank is a long metal rod that is slightly smaller than the hole. The end of the rod is poked into the hole, leaving a small gap all the way round.

The paste is then forced out of the tank, through the hole, and forms a tube that slides along the rod. When the whole rod is covered the process stops, the tube is cut into hoops that are then baked.

The process is called extrusion and the great skill is to get the mixture and temperature of the paste just right. Too sloppy and it slides off the rod - too dry and it crumbles.

Hula Hoops have a totally different meaning to us '60's generation - They are hoops of about 1" (25.4cm) pipes bent into circles (3 foot diameter)and joined by a piece of rod.
Arrange it at waist level, give it a spin and keep it gyrating by moving your hips!

To answer your original question - the "dough is forced through a nozzle, part cooked then cut to shape and finally cooked.