they rely on your experience in knowing how its done.
The rough opening is only rough, it does not have to be square and most likely is NOT. The opening should be but not limited to about 1 inche larger than the frame all around. This is where the shims come in.
You make the frame perfectly square via shims and a square. I normally try to do the shimming on the hinge side, this makes the lock throw go deeper into the rough opening framing. I do not like lock throughs only going into the frame and then into air. Kick ins are too easy.
Now, here is what I do. I shim the hinge side and place shims where the hinges are. Normally three hinges. Then I put some shims on the top also. I do not put shims on the threshold at all. Now I predrill some holes on all three sides about 2 feet apart. Then use a counter sink to counter each hole. On the hinge side, I normally remove one screw in each hinge and use this for my fastener. Use 3 inch screws. the screws become adjustment vehicles for you. You can actually use them to get to square. Apply all your shims then put a ninety degree square in each corner and find and secure square on all four corners. Adjust with removing or adding shims to get there. Once there and do a dry run to make sure the door closes securely and tight. check for light between areas.
When square found and door closes tight, then send home the screws not to change square but to only seat them into the countersinks. then spackle the holes for concealment.
Actually its very easy, but I can say that since I do this for a living. But, the very important thing is to achieve square. If not, the door will never work right and will leak.
Stuff in the insulation, saw off the shims sticking out. Install the molding and walla, your there.
Any questions after reading this, come back, very open to helping you.