You need to know that the window for dog to people socialisation closes at 12 weeks. And dog to dog closes at 18 weeks.
That means you have a very short time (given that the earliest you can legally take a pup home is 8 weeks) to socialise a pup. Unsocialised pups grow into very difficult and sometimes downright dangerous dogs.
Socialisation does not mean letting your pup run up to every Tom, Dick and Harry and being a complete and utter pest in the park.
It means exposing your pup gently to all the things it needs to be comfy with.
In these early weeks, pups are accepting of anything. So you want to make sure your pup is met by children, men, women, folks with beards, glasses, carrying umbrellas, everything.
And the 'meet' can just involve asking the person to give your pup a bit of kibble and a few kind words.
So - take your pup out (carried pre vax) amongst people. People love a pup but take care not to overwhelm. You dont want crowds of kids with their hands all on him at once. Just nice and gentle but as many different folks as you can pre 12 weeks.
People you know well - gentle handling and play with your pup.
Get your pup on car journeys, on a bus if you use buses, used to traffuc noise, loud bangs. Expose to all.
Now - the dog - dog - you dont want a pup that is a Royal pain, nor terrified.
So you want your pup to meet many dogs but play with just a few. A WELL RUN puppy class can be ideal to meet other pups - especially one where they let 5 or 6 pups have a few mins rough and tumble play and then break and do individual learning.
Your pup definitely needs to be able to have free play with a couple of other pups ideally or one or two friendly dogs that are owned by friends of yours.
This is how they learn bite inhibition fastest - pup nips, other pup squeals or dog will give a gentle bite back to teach the pup that nip was hard.
Be careful with this - once your pup is matched you can let them play fairly rough - they love it- but you certainly don't want your pup to have a bad experience so make sure you do know the other dogs' temperaments and dont put a small pup in with huge dogs.
Finally, never let your pup go flying up to other dogs you don't know. Both you and your pup will be very unpopular!!