And why don't they extend the dash vinyl all the way to the ends of the dash, rather than stop it an inch short where it looks a little un-finished? Don't know - they just do.
Remember that when you make the paper template, make it 1/4"-3/8" longer along the windshield rubber to make sure it'll tuck under the rubber lip so it'll look finished.
Liberally spray BOTH the dash (mask off the stuff around it or you'll have glue everywhere you don't want it) and the vinyl and follow the instructions for the adhesive you use. If you're cool, you'll mask off that 1/4"-3/8" along the front of the vinyl so it'll tuck under the windshield rubber easier later on.
You usually get about a minute or so to move the vinyl around and adjust it, then smooth it out by stretching around the curves and then use a wallpaper roller to get rid of any pesky wrinkles. If you're careful, you won't need the roller - it's just for insurance.
After it is installed and stretched out so the wrinkles are gone and you're satisfied with the ends near the doors (You DID roll the ends under for a more finished look, right?) THEN tuck the excess under the windshield rubber by using a couple of popsicle sticks to pry up the rubber strip and slip the vinyl under it a bit at a time across the width of the car. After a few inches you should get the hang of it and thank me for telling you to mask that little strip off.
Any adhesive that finds it's way to the finish side of the vinyl can be removed after it sets up by rubbing your thumb on it. If you're careful, that won't be necessary, either. If you get adhesive onto rubber parts, it can be removed by rubbing or with Acetone if you get desperate but BE CAREFUL as Acetone eats vinyl.