Parvo risk is highly local. Some areas are endemic with low vaccination rates and risk is very high just out and about in neighborhoods. Some areas have very high vaccination rates meaning high herd immunity and relatively lower risk. Ask your vet and call around to other vet clinics too for their observation about parvo in your community.
Some breeds are more susceptible to parvo than other breeds for no known reason.
The puppy vaccines are given as a series because the pup cannot get vaccine acquired immunity until their maternal antibody immunity has worn off. Assuming mama dog was fully vaccinated. It wears off at a slightly different age for each puppy, usually between 6 and 14-15 weeks of age. So each shot is attempting to minimize the puppy's unprotected time. For many (but not all) puppies, the 12 week-ish vaccine "takes" so in lower risk areas, many vets are OK with reasonable public exposure such as neighborhood walks.
Socializing on private, fenced property with vaccinated adult dogs where only healthy known dogs have been present for the prior year is generally safe. Puppy classes at a facility that requires vaccine records and sanitizes regularly is generally considered safe. Carrying your puppy in public is generally safe. Meeting humans in their homes generally safe.
Places like open dog parks, high traffic apartment or condo complexes with low vaccine rates, busy public parks and walkways, and pet potty areas at hotels or highway stops are all high(er) risk areas.