Wrap to toe rubber under the shoe and pull the overboot tightly back towards the heel.
I started with the arch, then pinned on the outside edge. For my wife's shoes, I needed to put in about one more pin on each side between the midpoint and te toe to ensure that rig doesn't get lifted of the side of the shoe by snow.
The Pearl Izumi Barriers have a velcro closure on the heel allowing you to access the shoe and finish affixing the rig to your warm feet. It's easy to pul the pins shown with a breadknife and switch to another pair of shoes.