Socializationis, in a nutshell, helping your pup become familiar with its environment. Puppies are not unlike children in that they learn a lot from early experiences — including how to relate to other dogs, in addition to other animals and, of course, people. It’s vital that these experiences are positive, and that there’s little to no stress or anxiety associated with them. Pups that are unsocialized often develop behavioral problems as they grow older, such as aggression towards people or other dogs, or extreme fear in unfamiliar situations.
The best time to socialize your pup is between the ages of three and 14 weeks. At this time, their brain is very open to new experiences, and they’re better able to learn appropriate responses to the world around them.
Read more at : http://www.sfgate.com/cgi-bin/blogs/pets/detail?entry_id=49291