To use a knitting belt, strap the belt to your waist or hip. Attach the extension belt if needed. Be sure the buckle doesn't fall in an awkward position on your back. If you choose, you can walk and knit fairly easily. If you prefer, you could strap the belt to your right thigh so that the holes are facing up.
Insert a double-pointed needle into one of the holes. It may take some practice to get a comfortable angle figured out, but once you do, the belt will hold your needle for you! Multiple holes allow you to use different sizes of needles, and you can use varying lengths of DPNs. I would recommend needles no shorter than 10” for maximum comfort; you shouldn't be hunched over your knitting.
If you choose to wear the knitting belt on your thigh, here's how you can customize your belt with the extension strap:
Put the knitting belt on your thigh, noting which holes are comfortable when wrapped around only once.
Attach the extension belt at the comfortable thigh hole and try it on your waist.
Be sure that you're buckling the belt extension to the knitting belt (as you'll now essentially have two belts hanging there).
When positioned, the pouch should be more or less over your hip.
When you're comfortable with the length of both the thigh and the waist extension, you could cut the leather strap to size.
Certainly, you don't have to cut the leather strap, but when you have it exactly the way you want it, you won't have to deal with any long ends flopping around.
I know this is a little hard to explain in text but should make sense when you get it and play around with the two pieces. I know that you will love this belt as much as I do!