Ok, step by step:
1) use hand #1 to stretch your penis all the way out to a good stretch and hold it there
2) use hand #2 to push the attachment tray all the way in towards your body
Note, you will need enough rods on the extender so that when the attachment tray is pressed all the way in, and your penis is stretched all the way out, the attachment point (noose, velcro, strap, etc.) is just behind your coronal ridge (base of your glans)
3) hold the stretch and the push. Use your unused fingers to attach your penis to the tray
4) slowly release the tray
That make more sense?