TMI Alert ...
1. The idea is to keep your young pup away from frequent dog traffic to avoid Parvo and Distemper infection, mainly. Most pups don't have full vaccinations until age 12 - 16 weeks. Before that time, they are susceptible, and these diseases are deadly, most of the time.
2. However, you can have 'puppy parties' and invite many people over to your house, 3 - 5 at a time, to socialize the pup with people. You want to control the situation a little, to make sure no one tracks in stuff from the outside. You can also discuss this with your Vet, because some places have a high risk or infection and some have a low risk.
3. In addition, if you are careful, then you can invite dogs who are up-to-date on all vaccinations to socialize with your pup, on your property. Again, discuss this with your Vet. We used to use my dog to help other people socialize their pups. If you're not sure, wait until your pup has had all shot before socializing with other dogs.
4. Any time that you want you can take your pup for a drive (pups may get car sick but most grow out of it fairly quickly.). YOu can carry the pup while shopping, and keep the pup in the cart... in places such as PetsMart, and some Home Depots. StarBucks lets you drink coffee outside with your pup.
Dr. Ian Dunbar popularized the general guidelines. I don't think he 'invented' them, but he did summarize them for general understanding.
Here are two free downloads:
http://www.dogstardaily.com/free-downloads