Not quite sure of the question.
Secure and use? Not to demean your question, but I kinda thought it was obvious.
Here's a pix of a double hook, I use the single one like you bought - fastened to the center of the appropraite rung(s). Although mine does not have the wheel on it. That must make it a lot easier to roll up the roof and then flip over so the hook graps the peak....BUT also presents a danger of being tripped on.

does this help?
If not, I'll take a pair of my old one in use and post it. I'd take a picture now, but it dark and raining outside now.
-Bill