Anyone know of a good how-to site?

I've borrowed a couple of Acrow props, so that I can safely get onto the top
of the conservatory, and finally re-paint, and whilst I know the principle
of where they go, and of putting timber on top to spread load etc, the
mechanism of the Acrow is a mystery to me. These ones have a sort of collar
with two handles and a grub screw, and a giant kind of chain link, which
obviously fits into the holes of the moving strut, and is used for leverage,
but I'd prefer some guidance before trying it for real.

Cheers

JW