
It IS very confusing when you start off! :) No, a best puppy win at an Open show will never qualify for Crufts. At Premier Open shows (they are few and far between) the most popular breeds may qualify by winning Best of Breed, and you can also qualify by winning overall Best Puppy in Show at all breed Open shows, or overall Best in Show or Reserve Best in Show. So in the great majority of cases, open shows do NOT qualify.
Junior Warrants confuses even me, but then it never happens in my main breed as we never have enough puppies shown to be able to gain enough points. Basically you count wins at open shows up to the age of 18 months (Best Puppy or BOB, has to be a certain number of dogs present, think it is 3) and class wins at championship shows. Somebody else will know much better than me!
A stud book number qualifies you for Crufts for life and you gain one in various ways -exactly HOW depends on your breed. You automatically get one by winning either a CC or an RCC at a championship show, or by gaining a JW. Then certain wins in certain classes also qualifies, such as a first in the Open class -but this must be at Championship shows with CCs on offer for the breed at that show. Popular breeds can get it by winning 1st, 2nd or 3rd in the Open, and also certain placings in Limit -less common breeds can only do it by the 1st in Open. There are different bands of breeds for the stud book which explains how you get it for your breed:
http://www.thekennelclub.org.uk/item/2852