For each of the many recognised pure breeds of dogs, there is a written standard, which tells us what we should expect to see in the "perfect" specimen of the breed (there is no such thing as the perfect dog in any breed, but that is what breeders are striving for). A dog that measures up to the standard is one that often becomes a show dog. This dog will compete in "conformation" shows against members of its own breed and against other dogs.
The competition is one in which the judges determine whether or not the dog is a good example of the breed and if, in fact, it is the best example of its breed at that show (this is the Best of Breed award) and if it is a better example of its breed than other dogs are examples of their breeds (these are the Best of Group and Best of Show winners). There are other awards too, like best of a particular age group, best opposite (this means if a male wins the best of breed, then the best opposite in breed is the best female). So just because a dog doesn't always win best of breed or best of group doesn't mean that he or she is not a good example.
As with all sporting events (and dog showing is considered a sport), it is all dependant on many factors - the day, the dog, the judge (some judges like different styles and they may not like the style of dog you have), and of course, the handler. Some people take the sport very seriously (sometimes too seriously, and these people take losing very seriously as well) and some approach as a hobby to enjoy and have fun with their dog.
At the moment, there are two standards for Chow Chows. There is the one that is in use in the United Kingdom and is used across most of Europe; and this is the same one we use in Australia. Then there is the one that is used in North America. This one is much more comprehensive and detailed. Included here are links to the American Kennel Club's official version of the standard, to the US parent club, the Chow Chow Club Incorporated, which has an illustrated version, and to the Victorian Canine Association (the state affiliate of the Australian National Kennel Club) version of the UK standard.
The Australian National Kennel Club - Australian Chow Chow Standard
The American Kennel Club - Chow Chow Standard
The US parent club, The Chow Chow Club Inc. - Illustrated American Standard