Socializing your dog whether it be a puppy or adult simply means introducing your pooch to other animals (including humans), things, places, and situations.
So when should you start socializing with your pup? It's best to start right when you bring your puppy home but should continue throughout the life of your furry family member. The critical socialization time is when your puppy is between 5 and 16 weeks old.
You want to introduce your pup to others (human and canid) gradually and gently by first introducing them to 1 or 2 friends and/or family members at a time; people who you know will treat the puppy easily and not be intimidating. Later on, you can start introducing your pup to more animated adults, kids, and larger groups.
"Puppy Parties" or "Puppy Socials" are the terminology some have coined for socialization sessions between pups. They should initially last only 30mins and work up to an hour before giving the puppy a break in his crate. The goal is to make these introductions in a relaxed and controlled environment at home before eventually bringing the puppy to other dogs' homes and out in busier public places. The end result is a dog who is well behaved around visitors and can be taken out in public without being a burden.
When making introductions of your puppy to older dogs ensure that the older dog is of calm temperament and up-to-date on all vaccinations. Both puppy and dog should remain on a leash at all times. Also, some dogs are not okay around strange puppies so choose your introductions wisely.