Putting it on is dead easy.
First take the main part- its the one with the huge hook attached.
Roll your foreskin back so that your head is fully exposed.
Place the main part on top of your head so its now wearing a very unusual hat
Roll your foreskin as high up over the cone as you can. If you can get your foreskin all the way up so it totally covers the cone, all the better. You need as much foreskin as possible to help the vacuum.
Now take one of the outer cones, one of the sizes will fit you best, trial and error will tell you which. Keeping your foreskin as high as possible, place the outer cone over the hook (the hook goes through the hole in the middle of the outer cone) and push the outer cone fully down.
You will now find if you let go with your hands, it will all stay on you.
If you pull the hook, you can now stretch away
Simple as that, and remarkably effective.
Any more q's just shout