Ok first you have to make an outline of the opening between the hood and the heat insulation. You just need it to stretch from the front to the back just past the second vent (approximately 7 inches from the inside of the L shape).
Next transfer the outline to the foam rubber sheet. The foam rubber must be at least half inch thick. Make sure that the outline thats transferred to the foam is just slightly bigger than the outline that you drew from the hood. Being a bit bigger (about 1mm beyond the outline should work) it will be clamped down once the it is installed in place.
Try to make the edges as straight as possible. This keeps little openings from happening because the edge is t straight when clamped between the hood and the panel.
Now being a rubber material it will dry up over time from the dry heat of the engine bay. I use some K&N oil to provide a light coating.
Then I install it in place. Make sure that you place the foam so that the middle thickness of it is on the edge of the panel and the top is secured to the top part of the panel by the hood vents.
Finally, you should test the leak by two methods:
1.) first shine a light thru the top of the hood into the hood vent and see if you can see light bleed thru. Seeing some white foam brighten up is fine just not actual rays of light.
2.) Then close the hood and pour a cup of water thru the first and second openings of the hood vents.
You should see that water does not drip into the intake compartment.
Spray some more oil every month or two to keep it from drying up and cracking.