How do I properly load a sub into a box?

There isnt anything special you need to install a sub into a box, just screw it in, there are normally like 8-10 screws to hold it in place, that should do the job

Some premade boxes come with rubber rings which ensure 100% sealing, but thats only with premade boxes and I dont know anyplace offhand that sells them seperate, I had one with my old Qlogic box.

As for the dimensions, the hole for the front should not be the size of the subwoofer, but probably like a 1/2 inch to an inch smaller. As for your case I dont know what they mean when they say the hole is 9 1/4, but if you are making the box yourself, just make a hole a little smaller than the diameter, maybe by like 3/4 inch, and then just test fit it, but you dont want to make the hole too big, cause then you are just plain out screwed. There is no perfect size though, each sub will be different, but most subs have a big lip on the top so that if you make the hole a little too big or a little too small you should be okay.

alot of subs have templates on the boxes, or detailed mouting dimensions

Use the box your sub came in as the template. It should have a inner cutout that the sub sits in.
You can also go to Home Depot or Lowes and get some double sided foam tape. This is what I used after routing the box so the speaker would sit flush. Just stick in on then tighten down the sub.
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Grab an electric screwdriver and and find some small basic wood screws and screw them in the holes. As far as the size goes I would guess you need the hole to be at least 9 1/4" but not much bigger or the screws won't meet any wood. Go to a audio store and see how the subs sit in their boxes, if they fit nicely (which they should because most subs are about the same size) measure what the opening is and copy them if you are planing on making your own and if not just buy them.