O'mike is right, but I should have mentioned that I prefer to use something like a GRK trim head screw for securing jambs (not a big gold phillips screw)- the heads are almost as small as a finish nail, but being a screw, allows you to adjust the jamb by turning in or out slightly and snug up the jamb to the shims. Just my personal preference- there are a lot of ways to do it. I like my door jambs to be as rigid as possible so everything doesn't shake when you close the door.
Definitely replace a top hinge screw with a longer one to take the weight of the hanging door.
i use nails. The doors I get comes with 3" screws to replace a few of the hinge screws with like Mike mentioned. Keep in mind, do not drive your nails all the way in until you are completely satisfied with the door's install. This way you can still take them out to make any adjustments.
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