What type of tubing are you supposed to use to make them? I have some black irrigation tubing that is about a half inch (?) thick.
That's the right kind! 1/2 in will make a skinny hoop though, what PSI is it? It should be printed on the tubing. If it's a lower number (120ish) it will make a light hoop that would be a little harder for a beginner to keep up. But you can weight it with water in the tubing (which some people find annoying), or even tape will add weight, and tape is easier to remove than water.